Last year when I put my embarrassing first set of samples together, I posted them up on the
Drawingboard - (a great forum for illustrators, artists, comic artists and hobbyists) I was amazed that our own
PJ Holden, amongst others, was willing to critique my work.
I've included a link to that forum posting
here 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.