I go through this every eight months or so. For me, the best way to break out of it is to do two things:
First, I reduce my chess playing. Burn-out usually occurs when you are playing just too much and the brain sort of goes on automatic as a result. Take a break from the game, even if just for a few days (I usually start playing a different type of game too).
Second, I like to switch to a different type of chess. For example, if I get burn-out with CC chess, I switch to live chess. The change of format can help clear your mind.
Right now, I feel like I'm in the middle of probably the worst slump i've experienced playing chess, and I want to know how to break out of it. I find that in many of my games I can't seem to concentrate, making miscalculations all over the board, losing games against opponents I could have beaten handily a couple of weeks ago. I've also noticed (after the fact) that I'm missing tactical opportunities consistently because of my recent inability to concentrate.
I almost feel as if i've regressed three hundred points, and it's disappointing enough that I feel like giving up on chess.
Has anyone else had this problem? Any advice?