First,be nice to everyone you meet here on dA (and in real life),there's a person on the other end of the computer and you don't know what they're going through.
Second,know the differences of they're,their,and there
-There:A location (It's over there.)
-They're:They are(They're going to visit Chicago.)
-Their: Belonging to them(That is their house.)
Practice:They're going to San Diego to visit their grandma who lives there.
Third:Learn to take constructive criticism.I don't mean the "You suck!" kind,I mean the "His chin's a little too low" kind.We all work hard on our respective crafts and it can be frustrating to hear what you did wrong but that's how you get better.That's right,your critic(again,if they're being polite) is trying to help you.
Fourth:Learn to critique politely even it needs a lot of work,remember rule one.Try to mention the good as well as the bad and perhaps mention helpful tutorials.
Fifth: Please remember basic spelling or use spell check,especially if you're a writer and especially if you're writing fanfiction.Sound out words if you must and remember that misspelling an easy word will make people take you less seriously than a hard one.
Sixth: Remember "Please","Thank you",and "You're welcome"