Here's what I did, after being away from school for a very long time:
I went to the local community college library, and looked through the math textbooks. I picked the lowest level book that I couldn't do all the problems in off the top of my head. It was Introductory Algebra (this also contained a review of the definitions of real numbers, irrational numbers, etc., which I needed).
I checked out the book (you can probably get a "community" card from the library even before you enroll). I worked all of the odd-numbered problems in the book (I had to check the book out several times). Then, I did the same thing with the Intermediate Algebra textbook.
Then I registered for College Algebra. I made an A, then I took Pre-Calc, and made an A in that as well. I'm taking Calc I next semester.