Wave management. It's something supports aren't necessarily required to do, but knowing how to manage waves can help synergize your ADC by a lot. Because it's something rather subtle and not really a requirement on supports, people don't write guides for these. However, I can give you a few tips on the wave control part:
In general, you would want your ADC to handle the entire thing on his own, unless he is absent. If he is absent, they usually want to just clear the wave under tower, then do anything else because getting engaged on with a huge wave of enemy minions is the last thing you would want to deal with. So unless your ADC wants you to push the wave (nah this hardly ever happens even if the enemy tower is like < 300 HP), you shouldn't touch it other than blocking your towers off, or just last hitting minions to slow down your wave.
If they are approaching your tower, defend it! Your HP can regen, not your tower's, so you are going have to defend it as much as you can before your ADC gets back, without killing yourself of course. If your waveclear is shit (hello Braum), get a head start. If your waveclear is pretty good, save your spells for last hitting. Unless your ADC is almost here, you should start killing off minions on your own right when the wave is 1/4 into the tower range so you have enough space and time to fend off yourself, your tower, and can still get tower assistance to help you fend off things. This not only saves your tower, but also a good deal of minion gold for your ADC and even yourself from ADCs bitching and whining about you taking that stuff away from him.
Ah, item builds. This varies depending on whoever you're playing, but in general you're gonna have to get some defensive stuff. Since those guides aren't too common because whatever you suggested is kinda specific, I'll give you some pointers here too.
For starter items:
if you are planning on poking the enemies' eyes out and/or FQC active is something you NEED.
your tank standard item, unless the lane is so poky that last hitting even once means RIP half of your entire health bar.
the passive path where you are in matchups where sitting there and do nothing would be the better go. Don't be afraid to use it on tanks.
I would usually get the second tier gold item before sightstone and the moment you first recalled. Stats are good enough to help you survive in lane and maybe some roaming for another 5-10 minutes.
For the sightstone, I heavily recommend that you get it as soon as possible, vision is key! The tier 3 gold item versus the sightstone "upgrades" are mostly based on preference and playstyle, but since you're not going to have item slot issues for most cases, I prefer the tier 3 gold items + an active. If the active item you are building your gold items into just doesn't fit your playstyle or is just something you don't need for any reason, go sightstone upgrade.
After getting your tier 3 gold item/sightstone upgrade and your upgraded boots, that's when you can (or actually, should) start getting other things. Most of it is dependent on whatever is happening in the game, so there's no specific order. Some AD champs are fed and is becoming a huge threat? Get armor. Some AP champs are fed? Get MR. No major threats? Something to help sustain yourself.
If you're a squishy little-damage backliner (I would consider Bard and Lulu as this category tbh but that's just me), go off-tank but at least one mana-regen/AP item would suffice, unless your team is so ahead that you're not gonna die even if you have zero defense. If you're tankier, go full tank. And since you're gonna be a bit short on money compared to your teammates, picking and choosing what to build is important. I like to narrow down on the item choices because good ol' optimization. What's a good item that costs the least, gives me the stats I really need, without getting much "waste"? Things like that. So in general:
is your typical armor go-to, has stats supports need, though the passive isn't that universal but hey, armor is what you need.
if you are melee because ranged supports don't need that active, or you honestly think just a FH isn't enough.
a very good and standard thing to pick up when you need MR.
for very nasty cases where you need more than just the locket.
I don't like it myself primarily because plain ol' HP and mana aren't that appealing. Active is something I never use because my team is usually full of chickens. Though if you want it you can get it whenever you feel like you aren't tanky enough in general, though IMO not a good first rush.
for those who love poking and shielding/healing at the same time. On Lulu it's really core, on Karma you can get it but IMO new censer would've been better since she can multi-shield, and on Bard on paper this sounds like a pretty good buy. Not good on Janna because she doesn't really poke.
for those who don't poke, but shields/heals A LOT. I don't think I have to go over this ever since Riot buffed it pretty hard.
for hyper defensive playstyles. I don't get this mainly because I am extremely terrible at using its active.
isn't that good of a buy anymore especially with the preseason where items let ADCs stack 80%+ crit easily, but is still not at all bad if you know your ADC isn't really ahead, is NOT rushing crit, or you felt the need to help him boost his combative stats.
There's more to pick and choose but those are the best, low-cost picks for supports.
Hope I'm not bombarding you with an half-assed guide as a post, but hope this helps.
vs heavy ad
more universal
also you can try with those