I'd say the more detail the dreamscape/characters you're envisioning the better. I'm it can work on any level of detail, but obviously it would be much better if you had a really good idea of exactly what you wanted to be created. Of course, like you've heard on this site a million times, it's all dependent on the person and the dream.

My suggestion for the second part, though, is try to get a good mental picture of what you want it to be like pre-dream. That way, you have a good motivation for a lucid and sometimes, that's all it takes.