Disclaimer: I've just started my first ranked season last week. I don't drill or anything, I'm just playing ranked for some extra fun. I also play Support primarily, and do quite well given a capable team. (And if my team sucks, you'll never hear me complain, I just do what I can - as is the fate of support, we go in together or we go down together...)
Anyway - on to training! If I was going to train for high elo this is what I would do:
Set up your training environment:
Your environment needs to be controlled so you can train for the things you are interested in, but also as similar to live play as possible. Use Custom game mode, but bring some friends willing to train with you.
Find a partner (ideally in your case three-partners) to drill with you in custom games. The goal is to face off in the same lane, in the same roles, with different champion combinations to simulate a real game in a controlled environment.
What to train (this can be done in custom 1v1 or 2v2 with bots filling the rest):
- Positioning vs other champs
- Harass (counter harass)
- Turret Diving etc...
Don't train it all at once:
Pick a couple topics and drill one or two of them often (daily).
Once a week, run a full game with your 1v1 or 2v2 group (at least until it's obvious which side is "winning") to put all the drilling into more practical use.
Like Esq mentioned when you train a topic, set up your training so that you have to rely on only that to gain your advantage. So if you are training farming - don't upgrade skills, just work on Last Hits with a timer, and work out how you did at the end of the session.
Identified a Weakness?:
If you find a particular nasty gap in your play, focus on it! Say you like to play Cait and seem to always lose ground against Sivir (a common thing in Bronze) - play Cait, get one of your buddies to play Sivir and face off to work on it.
Retrospective / planning:
After the weekly game, talk about what went well, what went poorly and identify training goals for the next week.