The easiest way to gain elo is to play champions that people can't counter like akali, tryn, kassadin, singed, shaco, lee sin, noc, and so on. Playing any champ that has high mobility and damage will increase your win chance. Learn these any of these champs moderately well, mvp1292, and you should at least be able to pull yourself up 1k elo.
I've been lucky lately because of one thing. I realized that my teams were always getting beaten by a Tryn (seriously, I was the only one who could kill him 90% of the time), so I said screw it, picked Tryn to jungle with and I've been doing fine since. Basically if your team is having a hard time killing a certain champ their team will also have a difficult time killing that champ.