What can I do to improve my mid game?

I'm high/middle silver elo but I can't seem to get over the hump into gold. I main adc but feel very comfortable top, support, and jungle.

When I get to adc I win lane about 90% of the time by various margins. I think my mechanics are definitely above average for my elo and I farm extremely well. 75 cs at 10 minutes would be below average for me. I am confident in my game knowledge and communicate the plan with my support so we are always on the same page.

I'm not trying to say I'm some god or anything I just know I'm substantially ahead of my elo when it comes to laning and mechanics.

That being said I really struggle with my mid game as an adc. Unless I really do some booty blasting I have a hard time transitioning my lead in lane to an ability to hard carry, especially when I'm the only one winning my matchup.

I would say the biggest areas I need to improve are knowing when to leave lane to try and group or get towers in other lanes and when to leave lane and stop abusing my lead.

Right now I feel like I focus too long on punishing my lane opponent and continuing to grind out the larger lead when I should be trying to push and take tower and make plays for the team.

Also I feel like I don't have a great grip on champions with mid game power spikes. Like if I'm a full item ahead at 15-20 minutes should I just be super aggressive?

The adcs I feel like I'm very good with are I no particular order: caitlyn, vayne, tristana, jinx, lucian, ashe, kalista, kog'maw, sivir, and ezreal.

http://www.lolking.net/summoner/na/36402866#ranked-stats I had almost 1200 ranked games last season.