USChess.org has a great article on how Christian Galwe increased 200 rating points in 6 months!
Here are a few of the recommendations from the article:
* Study your own games with an instructor
* Don’t study openings…study structures and plans instead.
* If you play blitz, play with a 5 second increment and always try to find the best move
* Review your blitz games just like if it were a standard game.
* Do tactical exercises everyday for at least 30-40 minutes.
* Keep physically fit.
