Thats pretty much the question.
There are two ways to become one:
1) You request it to an admin (thedude, editor, or lex_icon)
You send them a FunMail telling them you are interested in becoming an advisor. When you FunMail them be sure to include some good advice you have given.
2) You get promoted
If someone notices you giving a lot of great advice you may be nominated to become an advisor.
Factors that play a part in this decision:
- high advice ratings
- overall history
- communication skills
- amount of time you've been here
- overall attitude
- helpful in general
I guess that just about says it all. :)