I read a technique is to put yourself back in the nightmare and control the outcome. make the outcome what you would have wanted. that way you feel more in control of your dreams. ive done it a lot after i wake up from a nightmare. its hard at first b/c the last thing you want to is revisit it, but after doing it a couple times it gets easier. For example i had a dream that my sister was stabbed to death. so i went back to the situation, after i woke up, and changed it to what i would have wanted to happen, which is her not getting stabbed. Once you get good at doing that after you wake up you can even start controlling your dream when you're in it. for instances, last night my dream started turning into a war, people shooting up others, and while i was in my dream i thought to myself, 'i dont want to be in a war. and its my dream so i shouldnt have to if i dont want to.' and i walked away. and the war ended.