Here are some initial rules/suggestions, which I'm just pulling out of my butt and are subject to change.
Helpees 1. Is this for a high school English class or a 100-level writing class or an upper-level lit course? It's helpful to indicate the level of the class you're taking. 2. If it's the night before, no one is going to feel sorry for you, and even if someone wanted to help you s/he probably doesn't have time to do so. 3. Demonstrate that you've put some thought into this before asking for help.
Helpers 1. Don't write the paper/thesis for him/her. 2. Don't help people who don't deserve it (see #2 and #3 under "Helpees")
Everyone (including non-members) 1. NO PLAGIARISM! If you steal a paper from here I shall keeeel you. If you need your paper proofread but feel uncomfortable posting it publicly, you might be able to work out an e-mail arrangement with a community member (with plenty of advance notice, of course).