Search through your high school materials for notes you may have taken. Review them, if possible, to help remember the strategies you used to solve problems when you were first introduced to them.
Talk to old high school teachers. Ask them if they'd mind loaning you a textbook or printing off worksheets for you to review. You may also find math problems and answers online.
Start from the basics of high school and middle school math. Ensure that you understand these skills before moving forward, as they'll serve as a foundation for the items to come. These skills may include basic algebraic equations, simple geometry, exponents and fractions.
Work each day to complete a few problems, as this keeps math strategies fresh in your mind. Gradually increase the difficulty of material to include. More difficult problems may include geometric proofs and calculus equations.
Test yourself with practice ACT or SAT math questions. These tests are designed to encompass math problems which may be covered by basic high school students.
Review specific items listed on your college math course syllabus (as these materials become available to you). Consider addressing these items in the weeks immediately preceding your entrance to college.