From foruming 101.
Do: Read the rules first. Rules are there to be broken obeyed if you don't want to get in trouble.
Don't: Break those rules, duh! Also, don't TL;DR those rules. It's a one-time read for your convenience here.
Do: Post your first post in the "Introduce Yourself" subforum under the Newbie Area. Also give details on how you found this game, how long have you been playing, what element you like, small details on who are you IRL, etc. A good introduction might lead to a good stay here.
Don't: Post your first post in the "Nerf This Card!" subforum. You will pass of as some whiny newbie who join just because your anger gets the better of you and demand that Dim Shield be nerfed. Even if you said you've played this game for 5 years. Which is false, since this game has only been around for 3 years, by the way.