I have the same problem with remembering dreams and prolonging them. But the answer you're going to get from everyone is to keep a dream journal and keep trying.

I've found the problem with becoming lucid is that I get so excited about the possibilities that I forget to slow down and do what I had planned. It sounds like you're having the same problem. I think the thing that helps most is to just keep going over in your head what you want to do once you become lucid so then when it happens you'll think back to that. That's what worked for me anyways.