I brought this up awhile back, but here is an idea for those of you who've written lately about how to improve. This is not a cure all, but it definitely helps.
If you have a chess program such as Fritz or Chessmaster 10K, set up your board, turn on your computer, turn your program level to a strong setting, and play through the 1st 8-12 moves of your favorite opening or defence. Keep a paper and pencil handy and write your moves down. Continue playing against your computer, when your engine starts to gain the upper hand, use the take back feature and back up the position a few moves and try another line of play, continue to do this until get very deep into the game without falling behind. Doing this on a regular basis will teach you how to transition strongly from the opening to the middlegame. Learning how to handle these critical positions will make a big difference in your results. I've been lazy about this of late myself, but when I was doing it regularly it made a big difference, I went from the 1300's to just under 1700 in 6 months. As I said, this is not a cure all, but it helps a lot. 🙂