need some help in ranked please
So I have been playing ranked games as much as I can (8 outa 10 are ranked) and I have found myself losing more then winning (big surprise right?). I know in ranked you belong to the rank you are given till you get better and out grow the rank, but I feel like I have already outgrown it and am still trapped in it. I have read several tips and tricks guides and I try my best to use them as a guide line to help further my gameplay, but I still find myself losing. I ward well even though I main mid. I still buy and ward when I can. I know my role as a squishy assassin. I try and stay in the back and wait for people to engage in a team fight then pick off the carrys. I try and help my team focus objectives (sometimes to no avail).
I'm just kinda at a loss. I feel like there's something holding me back, but I can't put my finger on it.
Main lanes and champs. In order from best to worst
Mid:
and
I am equal at both
Bot supp:

Jg: 
Adc 
Top needs some work I use Akali, yas and vayne, but not the best tops sometimes I need to learn some tanks.
Any help is nice. Feel free to add me and message me. I'm not on 24/7, but I can chat using my phones LOL chat client at anytime. I have loads of lolreplays don't even know how many. So that's that. Hope you guys can give me some useful tips and help me become a better player. :D
Hope to see you on the rift!