Well, first tip I can give you is to take a break after a loss and play a normals or two. I tend to wait until one of my duo partners is on before trying to ranked again. Also, try sticking with the same role and champ up until platinum. Your winrates on Annie, Thresh, Lux, and Volibear are quite high, so perhaps staying as a Support and jungle main might be best, especially since those roles tend to have the highest influence in the game if played right (I am saying this as a Plat support main).
Secondly, I highly suggest working on map awareness, warding, and dying less. Look at the map and see where the enemy is or hasn't been. Try to deep ward their blue or red whenever you can (just watch for mid or bot MIAs so as to not get caught out since you could have walked over a ward yourself). Information can win games. Is the enemy jungler camping top now? Get dragon. Is everyone top right now? Push bot. Don't be scared to push toward inner after you get the outer if you are winning lane. There are two spots you can always ward on either side of the jungle so as to make sure your routes are covered. I can show you this in a custom if you add me (I won't have much time to spectate games though, I want to get to Diamond myself and need to practice >.<).
Lastly, is always focus on objectives. Kills don't matter (well, to an extent they do not). Whenever you analyze a situation, always consider what objectives you could get out of it. Don't think "oh, we could get a kill," think "oh, if this person dies we can get bot lane tower then dragon." Or "if we focus too much on this person, they could get herald, so it might not be worth it, let us focus mid tower instead." This of course really depends on where their jungler is.
Oh, wait, one more actually. :3 Roam a shit ton as support. A good habit to get into is to go mid after your first back if you support. Every time, even if no play might be able to be made. It gets you into a good habit and could potentially get your mid a kill or two each game. A good support does not stay bot lane all game, in fact, a support often times is not even in bot lane at all after the first 10-15 min. You would be roaming and warding.
Good luck!
