I've been around for 2 years and I was gone for a while S5, came back in the S6 preseason, and oh boy was it an adjustment. Rift Herald, the introduction of Juggernauts, some new champs and reworks, etc. I actually started playing Rift more(I'm an ARAM junky), but it was a struggle. I'm not exceptionally good at any role, I'm particularly bad at Mid for some reason, and I'm only particularly skilled at a few champions, otherwise I'm average with most champions and understand mechanics pretty well. This isn't to say I'm bad, I'd even say that I'm fairly good. But I also make tons of rookie mistakes, like stuff you'd think a lvl 3 might do and they'd learn from it, but I can be very good at other times. So that's just my situation with League as of S6 roughly. Now, as I understand it, every Role has the potential to carry, but it's more difficult for Support and Jungle. Top is the most varied lane, you can have pure tanks, pure damage, hybrid, mages, juggernauts,and also melee and ranged. Top is focused around forcing your opponent out of lane more than they force you out, in order to snowball, but not to push too much or you WILL die to a gank or roam. This is why Top almost always packs teleport, it's essentially 1 free lane recovery and potential to turn the lane and push them out quickly after you've been pushed out, or back to recover after pushing them out or getting a kill and put lane pressure(possibly with the help of rift herald buff). Support is the next most varied, with very diverse kits and utility, with a focus on protection and peel for squishy carries(even if the support is squishy too), you got your tanks that initiate and well, tank for their squishies, but you also have squishy supports which heal and shield themselves and allies, and both tend to have cc of some kind in the Support role. Supports tend to get the least gold, and experience, and love. It's the least popular role despite being extremely important? But it's so unpopular that fill literally means support right now because there's so few people actually choosing to be a support. You can get fed but it's actually the most difficult thing to do in the game. Jungle is the next most varied, with both tanks and squishier champions, but an emphasis on melee. Kindred is the only /true/ adc ranged jungler, but you can got just about anyone jungle with the right runes and skill. But it might be way weaker than actual junglers. Your job as jungler is to farm jungle in spare time, gank when the enemy has pushed a lane in or is ganking a nearby ally, deny the enemy jungler their farm while protecting your own(including objectives like dragon and herald), and in general apply pressure where it's needed. Jungler is a really diverse role, in that even within the same champ you can go different build paths for different sub-roles like initiator or split-pusher(Udyr is a good example). Generally if you're a tank it's still a good idea to go for some damage-tanky hybrid items or damage items, or as a high damage build to have some tankiness, you can't generally afford to lose too much of either unlike adc's or mages that can build full damage.(However I've found that damage+tank hybrid builds are actually incredibly strong in general, moreso on Juggernauts which are arguably the strongest champ type in the game if you ask me). Basically though you're a utility knife that can do a lot of things but only 1 at a time(you're either splitpushing or taking dragon or defending mid or teamfighting, but not 2 of these in quick succession, as a generality. Mid is the next most varied, you're really limited to mages or assassins, generally squishier. Inlane you're like top, trying to force your opponent out of lane, but then roam to other lanes for sweet bursty goodness, especially when you're fed, and it's a great snowball lane. You almost always have high burst and wombos but are vulnerable after, relying heavily on your team once you've burned your abilities to protect you until they're back up. I you dont have waveclear in mid, you're at a disadvantage, as pushing the lane quickly is important.ADC is the least varied, you're literally bound to being an AD champ if you're going to be useful at all, and you're ranged(except morde and some very niche, 99% of the time bad picks). Generally you're better off farming the entire laning phase and then coming out with a strong mid-late, but this can be hard if the enemy is aggressive and denies you lane with pressure. Even under tower though you can come back pretty strong as long as your teammates dont feed and let a super strong lee sin come under tower to one-two your ass into oblivion. You can snowball really well really early, if you get 2 kills within the 1st 5 minutes you can garentee an incoming enemy gank to shut you down, or a roam if your mid is behind, and you always have to be watchful of it because it can tilt you hard to get shut down by 4 people bot out to kill you. With that said, Vision is probably most important botlane, with dragon pit and how it's almost always the object of a roam(you see 1 top roam for every 7 bot) Supports are supposed to be in charge of vision, but a good team is always buying pinks as needed. Vision lets you play aggressively and snowball, but with more safety, having reliable vision lets you push hard and fast and destroy in lane and then avoid ganks so you can keep doing it more, and being aggressive helps keep the enemy from busting said wards, it really helps you keep your advantage or lessen your disadvantage to have better vision, and it's ALWAYS a battle throughout the game. As of right now my best advice would be, choose some champs you like for 2 roles you like best, and practice it, get a good build going, and always start aggressive unless you have a VERY aggressive laner. The goal to doing well right now is to outplay early, and carry that bonus to town for the rest of the lane, either by following up with more kills, or pushing them out of lane so you can farm and they cant and you get more fed and then kill them to death. If you mess up early, dont be afraid to play safer, more emphasis on farm than harass, you cant afford to try to be aggressive early and die several times, you can afford to die once or twice but farm well and come-back mid-late. If your laner tries to roam you can actually oftentimes get fed over their lvl and turn the lane/game. As for jungler(not having a lane) It's a tricky role with a lot of pressure to do A LOT within a short span, but it has really good snowball potential if you pick your ganks right. Also, almost always try to gank lvl 3 or 4, but pick it well, if all your lanes are doing well just farm some more, wait for the enemy jungler to appear and either help that lane OR go take the enemy jungle, you can basically always find a camp opposite where they are on the map, if they're mid help mid for sure, it's a very vulnerable lane and you want to help them carry. You need at least 2 people carrying in a match to win, so if you need to camp a lane to secure your advantage and a teammates, doit. Everyone hates being camped but if your goal is playing well, you abuse mistakes and play around weaknesses, which if that's an enemy feeding you and a laner, so be it. In relation to this, duo top is actually really dirty in lower-elo, but you need gold items and people forget this. But duotop early is unexpected and strong, you get really good lane pushing and harass, and ganks just turn into a 2v2. You will be ganked though as duo top, with extreme prejudice once 6 hits, and if the enemy jungler has an exeptional clear, you will lose the match. So just be careful of that if you decide to do that, only do it maybe on draft when you know the enemy jungler is not udyr.
I hope some of that was helpful and not just me blabbing. I can give some tips on a few specific champions that I'd say I'm above-average with(Aatrox, Nasus, Yi, Pantheon, Ryze, Kayle, Sona, and sorta Thresh.)
Etiam @Juggernauts; the reason they're so strong is because they have very good damage output and threat level, but enough tankiness to let them frontline and get low risk damage to the enemy, with Steraks and Titanic being the best examples of why, with health, damage, and burst-shield that actually makes you stronger, Steraks is an insanely useful frontline tool, and on certain champions it lets you pull some amazing stuff with 1v2's and tower dives. Titanic scales off health and does some insane damage(when you combined the base damage stat it gives plus cleave's on-hit every hit damage to the target and people behind, Titanic is awesome for both bursting(dat active does like 400 damage late-game) and sustained damage due to the cleave. Deadman's plate is a runner-up in that it gives armour and health as a full tank item but the passive means whenever you move between attacks you're adding some bonus damage to your attack(unlike shiv or rapidfire it doesnt need to reach 100 to discharge) as well as movespeed to help you reach the disengaging frontline.
dat comment length tho. sry.