How Do You Scale in and Scale Out of Your Trades?

I use the 20 period moving average on all my charts. I'm a bigger chart. As far as getting out, I really wish I would scale out. That's probably something that I should put on my list of things to work on for next year. Habits are hard to break. And I can't tell you how many times I cover something and go, why didn't I keep some? You know, but I think about it like five seconds after I've already filled.