How do I improve in League of Legends

Hey guys, Keiba here; Due to the years of playing league I've noticed a dramatic change in my gameplay & knowledge. Season 3 was my first season playing ranked and I ended up in silver. After that season 4 I went from silver to platinum, season 5 high platinum and due to Internet issues and performance issues (game play wise) I went back down to gold 3. I've noticed I get discouraged easily and can never stick to one role because I've felt as if I have tilted so bad that I'll never be as good as I once was or even better. Once an AD Main now an Mid Main. I switched to mid because I ended up hating the fact that I had to rely on someone in lane and couldn't carry myself. I enjoy mid lane so much yet I'm only mediocre, I can't ever seem to find one role and stick with it because I constantly feel as if I'm not good enough for that position if not that any position. I don't have any friends or players who are highly above me in skill, their either slightly better or lower in skill level. I do not have anyone to learn from or who could help me with improve and I was hoping from you guys that maybe some advice could help me. I'm just wanting to stick to one role, Improve, have a decent and stable champion pool and overall improve and excel at this game