Actually take time to look at the entire board and think it out before you move. My rating has jumped 100 points in just two days using this technique.
I'm pretty sure it will help my game rating too if I ever decide to apply the same technique to games!
I used to do the tactics at the Chess Tactics Server, but it doesn't let you look at the board! I learned some tactics, but I practiced bad chess by doing something that looked promising from my dismal perspective and hoped for the best.
I'm hoping to have the discipline to sit on my hands! I may try it literally if I find myself playing to quickly again!
My goal is to hit 2000. I figure 2000 tactics should be good enough for now and if I'm still around 1400 here, there's some other area where I really need help.
Perhaps by working through the Mammoth Book of Chess will do the trick, if not I still have a Purdy book that I think I can handle better this time.