Thoughts (negative and positive) are like seeds and they’ll grow. This can be good if it is a positive thought, but if it’s a negative thought we’ll want to catch them before they grow too big.
If I feel down or if I’m saying things or doing things in a negative way, I’ve found that most of the time I can trace my actions back to a negative thought. Once I’ve identified the negative thought, replace it with a positive thought or something else uplifting.
I found that when I traced my thoughts back to an original negative thought and then identified something to replace it with when it popped in my head again, I was able to gradually over time become a more positive thinker.