Blitz requires that you be in a certain mental state to compete well. Try playing in the morning, about 10 minutes after your first coffee of the day. Make sure you have breakfast. Make sure you're not tired. You can tell whether you are going to play well or not by doing a few puzzles on the tactics server .. bad at the puzzles? you'll be bad at blitz. If you start losing then don't play on.
Take note of when you are playing well, you should notice that your good blitz periods occur in cycles (mine is currently about a fortnight), in general i think the younger you are the shorter the cycle. Don't play blitz when you are having a bad day/week/month
Ultimately you can't take blitz too seriously .. its a bit of light entertainment but just like similar diversions (*cough* World of Warcraft *cough*) if you find yourself becoming addicted .. give it up.