Promo renders should be lighted well, showing off the product at best. Avoid too dark areas and too dark shadows.

Then show details and special features. If you're got nice wrinkles in clothes.... show them! If a certain part unbuttons or so.... show it off! Did you incorporate some of the figure's morphs.... again it be seen in a render.

For clothing I also would avoid an enviroment around them as much as possible. It's better to use nice backgrounds that don't distract. At times you would need an enviroment.

With ballet clothes I would show off the figure on a reflective plain floor with perhaps one mirror and a bar. No walls and such, just a nice background. Let the images focus on the clothes without to many distractions.

Artwork and 3DToons items, create the perfect place for you toon and other figures!

http://www.renderosity.com/mod/bcs/index.php?vendor=23722

Due to the childish TOS changes, I'm not allowed to link to my other products outside of Rendo anymore :(

Food for thought.....
https://www.youtube.com/watch?v=pYZw0dfLmLk