METAL IMPROV
Discipline. Don't judge yourself. Only play what you feel yet keep it simple. This isn't a show of how good you are but how much you can hold back.
Go back and listen to my exaples and realize that I am playing at my best as far as improvizing with control. I'm playing intetionally. Most pros won't let you see this.
So don't judge. See how over the course of an hour or two how much better your speek through your instrument on the fly!
Good Luck,
AJ