Seeking assistance to achieve greatness?

I'm gonna come out and say it flat. I'm a pretty bad player at league of legends. I've been trying my best, and i have improved a TREMENDOUS amount, but it all seems to be to no avail. This isn't something to complain about the AFKs and Feeders (hell, usually I'm the one feeding even though I'm trying my best), but rather a call for assistance. I've recently reached 30, and Ive fallen in love with the Ranked matches (though Ive only played about 5), and to my surprise, there were not near as many flamers as i thought. Everyone seems kinda chill and attempting not to flame and blame when giving me directions. I'm a Vi guy, tearing up the jungle with as many flying fists of fury as possible, but sometimes i just end up being some support champion who roams, dealing damage (unlike someone i know ... Not to name anyone.) I'm seeking assistance on how to be a better player all together. I try to be diverse in my lanes, having one decent champion for every lane/role (except mid because i don't have any good mid champions atm.) I main Cho'Gath top, Vi jungle, Nami supp and Kog'Maw ADC, and i do decent with all of them. I just don't know what i can do to help prevent feeding and assist my team more. I understand ranked isn't for me yet as I'm not too good in normals, and I'm trying not to be the guy i see so many people post about. If you have any advice or just some small tips for things like warding and builds (as i dont understand how to build Support or AP very well; my AD could use some work too), please reply with anything. There's no bad advice when asking for it. :3