There are two big ways you can gain Elo:
If you're significantly better than the people you're playing against/with, play snowball champions. Akali might be a horrible pick right now, but only if you're playing against someone that doesn't feed her. If you feed Akali, she's still going to wreck, whether assassins are viable or not.
And two, play with a good player. If you believe you're 1900 Elo, see if you can make friends with a 1900 player and duo with them. This might be difficult, but honestly, playing above the level you're at helps you the most. Just don't go "oh yeah, I stuck at 1k Elo but I really 2.5k player" and duo with Froggen or some ****. You're going to get your ass totally handed to you and it won't be fun. Set realistic goals - play a lot and try for, say, 1400 next week. 1500 the week after that, then 1600, etc. Once you hit a barrier, expand the time. Try for 1600 in two weeks. Then 3 if it doesn't work. Etc.