Its not much but i was 1k elo s2 and now preseason 3 im 1340 >.>. Maybe that can influence you! I Found out my normal game elo is much higher than my ranked so who knows. Play normals and get a feel for those matches, How do your allies/enemies perform in game?
learn from your mistakes and play champions who you have a better feel for mechanically. Try to play 3 champions for every role.
For example my 3 tops are
Teemo Cho'Gath Galio
My 3 Pref mids
Brand - Gragas - Karthus
Cho'gath - Nocturne - Skarner
Taric - Nunu - Nautilus
Im not sure if anything I have said helps you improve but if you focus on a core set of champions and improving upon your own gameplay as well as wiser decisions you can and will improve!
Also, try your best to avoid confrontations with your team. I swear everytime I have won a game with my team there has been minimal confrontations, if there were confrontations typically we Amend them. That said sometimes you have to take charge and help lead your allies. For example build suggestion or calling for teamates to group around objectives.
Best way to get higher elo i have found is to Protect all of your objectives, Control/Win enemy objectives and Lose as little of your own targets as possible In otherwords doing dragon with no deaths, taking a turret with no deaths, a successful gank, successful jungle stealing. etc etc.
If you are mid it is your responsibility to protect your Junglers jungle. If you are top you must ward yourself. If you are bot support ward!!!!! If you are adc farm and if you find it favorable to harass or follow up your support for a kill do so!. If you are mid play a mid who can protect themselves from ganks (e.g gragas) and above all else have knowledge of jungle paths and speeds. Essentially at 3:40 all junglers are up and ready for ganks some will come even earlier. Have a ward!!!!!!!!!. They wont always come for middle but some can afford to.
Another lower elo mantra : Above anything else, Feed yourself.