My requirements as a GM:

[list][*] General proper spelling and grammar. There isn't really an excuse, [i]especially[/i] in the Advanced Section, which specifically stipulates SPaG. If I see a character application that clearly hasn't even been run through a spellchecker, I immediately put my shades on (so I can take a dim view of the player).

[*] Being up-front about when they can (or can't) post. I'm happy to wait; RL always comes first. 

[*] Not being a dick. If I see somebody behaving belligerently on these boards and they want in on my game, tough titties to them. Speaking to one another with respect is a basic. I won't put up with anything less and I won't inflict assholes on my players.

[*] 'Getting' the game in question. It's kinda hard to measure, but sometimes you read a character application that suggests the player doesn't 'get' the game, whether it's because they don't know enough about the source (in fandom games) or because they seem to have a particular interpretation of it that just... isn't what the game is. 

[*] Characters with purpose. It can be anything, from the bleedingly obvious (Defeat the bad guy of the story) to the more tangential (Become rich could work in the same setting), but I really try to sniff out characters that are basically excuses for the player to explore whatever world the game's set in.

[*] Thinking about other people's characters. I love it when players work together to help one another tell their own stories and deliberately putting their characters in situations that will facilitate the development of somebody else's character. It's totally metagaming, but I don't like to think of RPing as a 'game' which can be 'won' but rather stories to be told from many angles.[/list]

I don't even mention things like being OP or godmoding because I normally block people from being OP by inspecting the character sheet and godmoding is so universally derided that it's a waste of pixels telling people yet again not to do it.

Looking back at this list, I must seem like an absolute monster. I don't think I am.

[sub]I hope not.[/sub]

The only one that's measurable is proper SPaG, and the rest of it is generally a gut feeling. I will reject a player only if I'm absolutely certain that I can't work with them.