Hey champ, I'm in a similar predicament to you. The trick I've found that's gotten my back up to about 950 from 800 and is keeping me climbing is to pick one role, and support, and get really good with two champs at both of those roles. Try your hardest to get your main role, and if you can't get it or someone would be shoehorned into support, go support instead.
The main role is going to be the easiest to carry with. Jungler is the best, imo, because people are dependent on you in laning phase more than you depend on them. Personally I main top, and mid works too, because you need help from jungling but otherwise are mostly self reliant during laning phase. ADC is a terrible idea because you rely heavily on a good support to not get your butt whooped. The point of this role will be to more easily carry a game if you have to. My Cho, for instance, can win top lane easily, get really big and really tanky, and turn a game around just by standing in front of things in a teamfight, even if the enemy team is somewhat fed.
Support, on the other hand, is the right backup because regardless of what anyone says, a support can carry. A good support can scale into late game even with a bad adc, while a bad adc is useless without a good support. It's just not apparent when the support is carrying because they don't get a lot of kills, but when you're spoon feeding kills to your teammates, you're carrying them. Vision wins games, and the supports hold the wards. Etc. etc. You need a good support throughout the game, and given the choice between shoehorning someone who doesn't want to support into it and doing it yourself, be the support. Your games will go a lot more smoothly for it.
I hope this has helped. See you on the other side of 1k elo.