How to increase your rating fast ?
If you are rated less than 1800 and really want to improve...
Do daily tactic : On the net (Chess Tempo or Chess Tactics Server) or whith your favorite program (CTB, Ct-Art 3.0, Chessimo) but train every day.
Not less than 15 min a day. Preferably one hour a day : half hour in the morning and repeat later. Train your tactic muscle. No rest day ! Do this for 21 days at least !