Doubt About Music

What are the rules for Fair Use in Copyrighted Music?
I need a clear idea of the rules that apply to fair use in music, so, correct me if I'm wrong, or confirm if I'm right. And I am talking about copyrighted music, there are no doubts about that, it is not public domain.
The music must be no longer than 30 seconds long.
It must be for educational purposes.
You must not be making profit off of it.
Is that all or is there more that needs to be covered? Thank you!
http://en.wikipedia.org/wiki/Fair_use
There is no definite length or use, and under certain conditions, profit can be obtained for such things as parodies. Each is evaluated on a case-by-case basis, so it's very hard to say something is fair use for sure.
You might want to read that all... but here is some parts.
In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include:
1. the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
2. the nature of the copyrighted work;
3. the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
4. the effect of the use upon the potential market for or value of the copyrighted work.
No Doubt - Underneath It All ft. Lady Saw