Well, I learned that the hard way!

But on topic, NEVER jump right to character making and trying to make the best character evar. I've learned that by now.
Here's a whole list dedicated to making the RP playable, enjoyable, and complaint-free for newbies like meself!

1. Get to know your fellow RPers. This is very important in learning where and what to do to make a character who won't be considered a Mary-Sue/Gary-Stu or avoid any rule-breaks. Put the rules into a document so you can see them whenever you need them.

2. Never throw chtspk around, it makes you look trivaly uneducated, and quite frankly, makes your posts hard to understand.
Here's an example of a regular post here:
Thundersail wandered the lush jungle, looking for something to eat, as his stomach rumbled like an earthquake and twister having fun. He wanders the almost blackened green trees untill he finds the rotting caracass of an Ankylosaurus with Velociraptors feeding upon it. He scares of the much smaller carnivores and rips into the warm, bloody and tender Anky flesh. He devours it and continues on his way, when he spots a Tyrannosaurus hunting. He passes the massive beast, not needing more wounds.
And an example of newb posts:
Player One: As Ardy grazed, he smelt allosaurs on the horizon. Knowing their tactics, he heads to the forest and enters the thick trees, safe from te preadatory dinosaurs. He grazes the wet ferns, the water releiving his dry gullet.
player two: te allosuar leped at ardy and killd him instantly an ate him
Player One: whut. I'm in the middle of the thickest trees, you can't kill me, let alone reach me. Plus you aren't even giving me a chance to do something about it!
player two: yes I can my charrie can do anything, and ur charrie sux, ply as a allosuar, they kik ***
Player Three (Admin) Player Two, I sugest you look at the rules before jumping into the RP like this. Plus you can't chatspeak here anyways.
player two: i can't understand u, spk english mother******!
*Admin has IP banned player two for breaking multiple rules consecutivley*
Player One: Thank you, admin! Here, have this chocolate chip cookie as a token of the RP'ers graditude to you. *gives admin chocolate chip cookie*
Player Three: Why thank you. Here's a cookie for you, for handling the situation so well: *gives another cookie to Player One*
Player One: Thank you, Admin! People like you deserve your status.

Oh, and that also bring us to Rule 4.
4: Never disrespect an admin, mod or even another player. It can lead to suspension or banning, maybe even IP banning. (If banning and IP banning are the same thing, I'll be quiet.)

5. Respect other players wishes. Never force people down your path in ANY locale.

6. Never kill another person's charrie without their permission or while their on a vacation or holiday. It's rude, as well as GM'ing unless the person says "You guys can kill this guy off now."

7. Never, EVER think you charrie is invincible and can blow up the universe. It won't happen. EVER.

8. If you beat another person in a fight, think of letting the wounds sink in to your opponent. It aint fair to kill everyone you fight.

And finnaly 9. Always speak with the player of a character if a fight scene should be needed to decide an outcome that satisfies both players.