As a former 800 elo player who is now GOLD III I can give you a few tips
1) CS and objectives are more important than kills ie learn to last hit, ward, and play safe
2) If you die 1v1 don't try to fight them again unless you recieve a gank from you jungler
3) Don't support at low elos
4) Know how your champ scales. Akali needs kills early so get them or you will be behind. Same with Lee. Singed will scale with just farm. So will most tanks such as Sej, Amumu, and Malph. These are generally safer picks as you can play safely and out-scale your opponent.