First of all I think this forum is great, and there are a lot of really good bits of advice floating around in it. I think a lot of beginners and intermediate artists should make it a habit of not only posting in here, but checking out other people's threads for those great nuggets of advice. There is the occassional redline sketch or paint over that really shows some great advice that is applicable to lots of people. People get burnt out a bit on repeating advice, so if you aren't getting in depth crits, look at other threads that may already have covered very similar issues in more depth.
Also, I believe this forum is best for work that you've already made a sizable effort on. Posting a rough sketch, or even a more finished sketch of only a single figure with no other background elements, well those might be more valuable in the sketchbook forum. Start a sketchbook thread and seek advice there for those types of works and I think you'll get better results.
It's also good to give us an idea of particular areas you think you need help. It gives people something to focus their crit on. A general "please crit me" will probably get general suggestions rather than the specific advice that will help you improve.