Last year when I put my embarrassing first set of samples together, I posted them up on the Drawingboard (http://www.drawingboard.org/) - (a great forum for illustrators, artists, comic artists and hobbyists) I was amazed that our own PJ Holden (http://www.pauljholden.com/blog/), amongst others, was willing to critique my work.
I've included a link to that forum posting here (http://www.drawingboard.org/viewtopic.php?t=64598) as I believe it is instructive, both from what someone should expect to hear upon posting samples, but also as an example of the sort of helpful criticism that needs to be given.
Sorry for not picking this up sooner.
There are some good comments there, especially from PJ Holden. There is no direct film/comics parallel but I suppose part of the artist's job is similar to the cinematographer's and framing the "shot" and or getting more dramatic angles is definitely something to keep in mind.
Also good tip on making sure it is clear the judge isn't Dredd when you see him - something I'd not really thought about.