A simple related habit -- though I didn't really evaluate whether it's useful, so maybe I am just fooling myself here -- is to translate your ideas into words without negation; into direct words. Instead of "don't forget X" say "remember X". When you do it for a while, it becomes easier. I think something, notice that it contains a negation, and think the fixed version.

The idea is that some part of your brain may extract "forget" from "don't forget", but the "remember" instruction always remains a command to remember.