Help me improve please
So I'm back once again to ask for some advice and stuff and such and what not. So what I am seeking advice on is how to improve myself as a player in ranked. Long story short I'm in bronze 5 once again and would like to at least make it to silver 5 before the end of the season. I'm not aiming for anything higher then that because 1 my computer is shit and I'm lucky to get 30 fps and 2 my internet is shit.
So I'll start by saying I don't main any role. I play all of them cause in bronze 5 people are always bitching and auto locking so its just easier to be flexible. So my roles go as follows: top being strongest, then support, then mid, then its a toss up between adc and jungle. My laning phase for everything besides jungle is all fairly strong. I know how to last hit and manipulate minion aggro. I understand how to zone and deny CS. I ward and don't over commit for kills I can't get (usually anyways). I almost always alert my team when my laning opponent leaves lane at any time and so on and so forth. My problems don't really start until around 15 to 20 minutes into the game.
I have a ton of trouble with the mid game and securing objectives. I know wards play an important part in the mid game and when I'm support I try to push up and get deep wards to be aware of enemy movements but the wards never seem to spot anyone. When I'm top or mid and take my tower I try to rotate and help my teammates take their tower but somehow we usually end up getting killed in a 3v2 fight that we should die in or something stupid like that. It just seems like once I reach the point of mid game something always goes wrong. Also my team never ever ever groups for anything. and idk this is part bitching (yes I know I deserve to be in bronze 5, not saying I don't just saying I wish some people would realize its a team game) But I seriously want to get better and climb out of bronze, cause I've done it before back in season 3 but now bronze just seems a lot worse since then.
As far as champions I like to play, for support its almost always Annie. I like her ability to make picks and secure kills by herself. For top lane its usually tanky support champions like Maokai or Lulu and the occasional Vlad or Swain. For mid lane its usually Vlad or Zed, although my Zed isn't all that great. For ADC its usually Sivir or Graves since they seem to be the meta right now and for jungle its Nunu because I'm not comfortable on Sejuani or Gragas. Also on a note of champions I have Hecarim but I'm a bit intimidated to try him cause every time I do I usually do bad.
Anyways, any advice will be greatly appreciated. And sorry this is so long and random. just tried to throw out enough information so I could get some advice that will be useful to me.