Identify the gaps in your knowledge. Ask yourself a few questions: "What was the last math class I took in school? How well did I do? If I opened my old algebra textbook, would I easily pick it up again? Or would I be lost?"
Memorize the fundamental algebraic properties: commutativity, distributivity and identity. Familiarize yourself with polynomials, imaginary numbers, exponential expressions, logarithms and square roots. Pay special attention to the quadratic formula and linear equations.
Buy a geometry textbook. Learn the definitions of terms like point, line, ray, and so forth. Memorize the Pythagorean Theorem.
Learn the trigonometric ratios and identities, including sine, cosine, tangent, secant and cosecant. Make sure that you understand the unit circle and the concept of radians. Now is a good time to learn about the binomial theorem and polynomial expansion. Learning about Pascal's Triangle can help you here.
Now it's time to tackle calculus. To get started, try to gain an intuitive understanding of a limit. Then learn about derivatives. When you can confidently solve basic calculus problems, you're ready to learn about integrals.