1. The ability to spell.
2. A brain.

If they have a genuinely friendly personality but don't try too hard to fit in, that's ideal. It's annoying when newbies just create a thread full of stupid smileys and then become "friends" with other people in 5 minutes, like so:

Yuna_4554: OMG Tidus246 ur avie is amazn lets be freinds!
Tidus 246: okay lol ill put in my sig we r freinds lets go spam newbie threads togethr.
Yuna_4554: Yay im aceppted!

Just be yourself and odds are you'll fit right in. Unless yourself is like what I just posted. Then you should be quiet.