I main mid and I take every opportunity I can to drop a ward near my opponents wraiths (both on Blue or Red side). This spot covers 5 commonly-used pathways AND provides vision of Wraiths, which is key to track enemy jungle movement.
https://pbs.twimg.com/media/Bw5HdLhIEAAwgwj.png:large
What about top, jungle and bot? What do you focus on keeping warded?
Support main
1) Between Dragon and the ramp, to give extra time to prepare for an incoming gank in bot and sometimes mid. Most just ward the bush.
2) Pink ward in the bot Tri bush if we're blue side. Easily defended defensive ward, and red side likes to green ward it so now I have vision of it and kill it.
3) When I can finally roam support I pink the bottom center bush in the river if I'm blue side, and the bush on the ramp if I'm red side (mid can defend it).
If Zyra, I can put a seed in the red side tri bush from the river.
Top lane. And like all the lanes my ideal warding spot depends on where I start and how aggressive I plan to be.
Blue side- Aggressive/winning
Tri-bush, warding off ganks as well as my laning opponent possibly coming for a gank. The minions/me will see them leaving through river.
Blue side- Defensive/losing
River bush, as far into river as I can. If I think I'll be tower dived often I will probably burn a bit more gold to keep blue-buff warded as well.
Purple side- Aggressive/winning
River bush. Possibly enemy blue buff if I'm far enough ahead to roam. Always good to apply pressure to your lane and their jungle.
Purple side- Defensive/losing
Tri-bush, as well as the lonely river bush by mid if they aren't warding it themselves. If I'm losing I never want another lane to be brought behind because of my shortcomings.
With pink wards specifically, in solo q, I will always get a pink on the closest buff near me to help my jungler clear counter-jungling wards and counter-jungling attempts. Every time.
Top lane, i keep the tri-bush warded always no matter which side im on, its a constant battle. I also ward the river bush whenever i can depending on which side im on. I will also ward either their red or their blue depending on which side im on if im winning lane or if they are out of lane.
That is a very nice spot, now that you've pointed it out. I'll definitely add it to my ward-this spot list. Thanks!
As support, I try to keep bottom Tri-bush and Dragon area warded.
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I main support so for my wards I get the bush above outer turret, the bush in the river, and between the dragon pit and the entrance to the enemy jungle. (This if I was on the blue team.) 
Wards? What are those? Oh wait, I am in Plat now, I can't use that excuse anymore...
All joking aside, when I play Mid, I like to ward in the bush on the opposite side of Red Buff. It may not give me as much vision as Janook's, but it allows vision into that bush which I find helpful, especially when on purple side and we need to know where the enemy is when doing Dragon.
When on blue side, I like to just keep it in the death bush, the small one in the river above mid lane. I feel like most Junglers try to avoid walking near dragon since it is usually warded, therefore giving away their location... but Baron isn't often warded early in the game and allows Junglers to roam through that river with ease, so I feel a ward is needed just in case a gank at top fails and they swoop down to mid straight through the river.
I've strayed away from maining a position, because what are the odds you'll actually get it in game? But my best role is Support, so I'll share my personal warding insight to the bot lane.
Two spots I always try to ward, regardless of side and having an advantage/disadvantage are the river brush leading into bot lane and the mouth of the dragon pit. Both of them provide info onto whether a gank is incoming and where their jungler currently is, and the dragon ward provides objective control.
I will usually put a defensive ward in my side's respective tri-brush, if I feel like their jungler may try to dive us or come around backwhen we're pushed up. The only time I aggressively ward a tri-brush in lane is when I'm on purple side and we have a lane advantage, then I'll go and ward their tri-brush. Why? I don't know, I just do.
Depending on how the enemy plays, I might make the two in-lane brushes more important in terms of ward priority. If their support chooses to play the game of "sit-in-the-side-brush-and-play-mind-games," then I'll usually talk with my ADC about one of us maintaining vision on the river and the other on the side brush in the lane.
Lastly, if either outer turret gets destroyed, I'll focus my wards on the tri-brush and entrance to the lane right by the turret.
I prefer top as of late, one of my more key spots to ward other than river for blue side is in the bush at blue buff and tri brush on purple/red side. I typically use a vision ward for those :)
Jungle Where to ward? Their jungle.
Support: Green blue side tribush and between dragon and blue buff. Yellow in bottom bush. Pink the bush behind red buff or behind wolfes.
Top: pink in center river bush and yellow in redside tribush
I main top. My warding always depends on where I am keeping my lane and if the enemy has stealth. If it's an Evelynn jungler on the opposing team, I usually just play defensively and ward as such.
I am on Blue Team: -If I push up, then I ward tri-bush closest to Purple's Turret. -If it's an even lane, I ward the bush on the edge of the river. -If I play defensively or I get pushed up, I ward the tri-bush closest to my turret. ---If I plan on playing defensively for the remainder of the laning phase, I get a pink. ---If enemy has stealth and I am playing defensively, I ward the blue buff golem as seen in the picture.
I am on Purple Team: -If I push up or the lane is even, I ward the bush on the edge of river. ---If enemy has stealth (except for Evelynn), I ward in front of Baron. -If I play defensively or I get pushed up, I ward the tri-bush closest to my turret. ---If I plan on playing defensively for the remainder of the laning phase, I pink the bush directly north of our red buff.
I main Marksman and my #1 spots to ward are the river bush, or the lane bush if I am pushed to tower. If I am purple side, I will ward the tri-bush a lot more as the jungler tends to come that way.
When I play Mid, I ward a lot. I also like to ward the area you showed. But I will ward whichever lane bush opposite of the wraith camp often in addition to it.
Top lane. Tribush if I am purple. River bush if I am blue.
Jungle main here. Warding as a jungler is difficult, because the areas of focus are ever changing.
-Is Dragon up? Ward the death brush (little river bush, pink ward is best) and into the enemy jungle.
-Preparing to Baron? Pinks and sweepers near the baron, and wards into the enemy jungle.
-Are the enemies buffs spawning and you want to contest, get wards near the camps and near the close lanes.
-Trying to counter-jungle? Wards deep in the enemy jungle.
-Defending against the counter-jungle? Wards near all of your the jungle entrances from the river.
-Are your lanes in particular danger from the other jungler or roamers? Get vision to the most vulnerable spots.
And these are just some examples. There is so much to cover that a jungler cant do it alone, and that is where having laners help is essential. Laners who what help from the jungler have to give them the opportunity to do so, and the easiest way to do that is keep vision near your lane, and try and keep track of where the enemy is placing their wards. This helps the jungler to know how to approach when they do come to gank.
Another thing for everyone to take note of, Jungler or other wise, is that while vision is great, communicating what you see is even better. Always use your pings when you see the enemy jungler or a roaming enemy. Even better if you can use chat. This tells the whole team where the enemies are and that information can be used throughout the map.
As top (blue side) I sometimes pink my tribrush if I'm worried about getting camped. It also frees me up to ward river brush over the wall if I want. I sometimes ward in front of baron if I'm worried about jungle invades. In that case instead of warding river bush I ward either a lane brush or enemy tri, depending on side.
I main Ashe, who -- as you all may know -- has limited escape. Because of that, I tend to ward any of the brush covering the river or adjacent to the towers nearest lane.
This helps give me some time when ganks occur, allowing for a slight head start to run away or engage accordingly.
I am mainly mid/support:
While in Botlane i keep the totem' s ward at the early stages of the game for warding the enemy bush, in case we get locked in the middle of the lane, while i keep the Stealths for the blue ramp or the tribush if we are pushing and the ramp is already warded. Vision is placed either at the ramp or at the tribush depending which one is not warded. If the enemy jungler is a jumper that likes to do sudden ambushed i get more cautious and ward crossroads in our jungle, if i can.
While mid i always ward a side and then keep the most near possible to that one, so in case i get a gank from that side i cans prevent it; warding dragon too, and sometimes the side bush behind the trees for jumper junglers.
But it depends a lot to enemy composition, there are my ways to go ^_^
I'm a mid lane main as well, specializing in Vel'Koz. Generally I like to ward that single piece of brush nearby Baron and Dragon, as it offers me a chance to prevent ganks from other angles than simply the brush closest to mid lane.
I don't really main anything, so...
Top: River bush or tri-bush, depending on which side I'm on.
Mid: I like to ward the jungle exit where the "banana brush" used to be.
Jungle: I like to pink ward one of my own buffs, if my opponent jungler is someone who might try to invade. Everything else is situational.
Bot: I always keep the lane brushes warded, usually prioritising them over the river. On blue side, I pink my own tri-bush.
EDIT: Oh, and one more general tip. Now that Oracle's doesn't exist, don't be afraid to plop a ward just in the middle of the river. I frequently do this around dragon and baron, since it gives me earlier warning of an incoming gank than sticking wards in the river bush would.
My main role is either top or Jungle, but my support is nice too I think. First priority for me is a pink get it out there and as deep as possible. Tri, their blue bush, and red bush.
I am determined to know where the sneaky jungle is and use that knowledge.
Thanks for the ward placement @Riot Janook ill make sure to keep this in mind when I am playing!
I usually fill; used to support main, but from how terrible/inefficient my warding is you would probably never be able to tell (first buy sightstone = ward spam). Recently I'll go for mid or top if I can, but I can also manage ADC, and jungle if I'm in the mood and support out of necessity, contrary to my old main (lately I haven't felt like I can make as big an impact as I used to as support).
Top lane: depends on the champ I'm playing, but if I'm shoving out I'll try to keep river brush warded, maybe drop a pink on our blue just in case. If I'm shoving really hard I'll keep their tribrush warded as well. If I'm playing passive, I usually won't ward anything since I'll just freeze lane in front of my turret (and I'm usually playing a tank that can escape a gank. If I'm low I'll ward my brush or just back and tele back). Purple side I'll try to keep my tribrush warded, usually pink if I'm at least somewhat pushed out.
Jungle: depends a lot on how the game is going. I like getting deep wards if I can, river wards when I can't, and defensive wards if I'm really against the ropes/the other jungler is running amok in my jungle. Favorite pink ward spots are in the side brush next to the enemy blue side; basically instead of warding that brush in the middle of river, ward the brush right behind it, between mid and their blue; not as many people check there for pink wards. Also on the brush near red buff, either closest to the respective pit, or between/behind their double golems and red (not the one attached to the red camp) are some of my favorite pink ward spots; the former gives good vision, but the latter especially hardly gets checked for wards.
Mid: The ward you mentioned is great; I hardly get that deep though, so I usually drop it just over the wall at the entrance to river. Also try to get the brush between mid and their blue if I can manage, or just a side brush.
ADC: I usually just save it for side brush control or river brush/tri brush control depending on what my support is warding, etc.
Support: ward all the things, as inefficiently as possible, lol. If we're blue side and we're pressuring them/winning lane really well, I'll typically try to take a stroll in their blue jungle and put some deep wards in (I'm usually playing a sort of tanky support). I'm pretty bad at purple side.
I main top in spirit, but I usually fill in botlane.
So for top, there are several spots that need good warding:
Top brush
Top tri
Baron doesn't usually need wards early, but always good to do for preemptive mid ganks
These are basic no effort wards, but if you are looking for deep coverage:
Enemy red (usually at the beginning of the game, if you're really ahead and gutsy do it after 6)
Pinking top side river bushlet
Enemy blue (same as red, but a lot harder for purple)
But overall, top doesn't ward much :P
I ward the river bush as top lane because im almost never pushed up to my opponents tower so its more just there of force of habit just in case I ever do push... But aside from that I just ward where I feel like my team needs vision most, if im filling my other two roles of jungler or support
