I'm not good enough to actually give out pointers that matter, but from my own personal quest to better the renders, I think...

1. observe - are you trying to capture reality, or to improve on it? Details can make your pic.
2. Lighting - can do amazing things with depth, contrast, and coloration, not to mention   cementing' backgrounds into the picture.  
3. Textures - my big weakness...if I ever get good enough with this, I threaten to deluge freestuff..;)
4. Know your tools - another big failure of mine. I'm not even sure where the cloth room is in P5...;) The
       more you know, the better your options are.
5. (Heresy alert...;) Postwork. It's like makeup (I presume) - just enough to make it look better,
       without making it obvious why that is...;)

Hope that helps. Now if I could just follow my own advice...;)

I wish I'd said that.. The Staircase Wit

anahl nathrak uth vas betude doth yel dyenvey..;)