I have gone from quite short-lasting images (or “movies”) to realizing that Im in the middle of a dream. The problem is that if I am not sleepy or relaxed enough, it all dissapears due to knowing what I see is in my mind. And if I’m realaxed enough to control the exitement, I soon fall asleep, loosing the control. 
I guess I just have to practise 'til I get it right no matter the state of mind, but any tips would be great. (I know its hard to give such advise since only I know about my own mind and myself though.)