I'm gonna try to cut down on captain Creek's original guidelines.
Avi don't have to look like your characters (some captains like to dress up though ^^), but that isn't really about roleplay....

1.) If your character speaks "Use quotations"
2.) For actions or whatever else in character, i.e. in roleplay just type it out like this without quotations or any special markings.
3.)Out Of Character (OOC) should be in ((some)) [form] of [[brackets]]

Here's a seriously lame example:
Kisuke had just sat down for tea, when ninjas leapt out from the shadows to attack. Calmly sipping his tea first before he said "No one interrupts my tea time and lives..." Kisuke dodge their blades and killed them all.
((I'm awesome.))

Notice all my in character goodness is actually roleplay and all my OOC nonsense is kept in brackets. You can even use a special colored text to represent your character if you like. I do.

Finally, and this is very important, Don't use info that your character WOULD NOT KNOW. Like just because while talking on PM you and another guild member say hey, we should battle! Doesn't mean your characters would know, you would need to issues a challenge within the roleplay. This also goes for people's abilities, especially their shikai and even more importantly bankai (which everybody who knows bleach knows that bankai is a huuuuuuge secret).

The heavier stuff comes later, when you get into the more serious roleplay (when you graduate!).

Regulars and crew feel free to add any helpful hints. I'm sure you're all going to spam my thread again anyway....