One of the best pieces of advise I can give you is....
I've been in the hobby industry for about 15 years, worked in Hollywood before that (as a scenic artist) and have been building models and dioramas ever since I was a kid.
One of the best pieces of advise I can give you is to just walk away from your model once in a while to get a fresh perspective. Read the whole piece at;
http://www.dioramasplus.com/site/?page_id=14/tips-and-tricks/one-of-the-best-pieces-of-advise-i-can-give-you-is
Cheers!
Randy Pepprock
Dioramas Plus