The best approach is an algebraic one. Learn all of the rules of arithmetic (including things like exponential identities); learn about polynomials (the factor theorem, the fundamental theorem of algebra, et al), and get to grips with solving general equations and manipulating math. Algebra is basically the language you will do all maths in, at least nowadays. Also learn about arithmetic and geometric series and the binomial theorem. You then want to learn about some of the basic theory of functions; learn some useful functions such as sin, cos, log and the relations between them. I barely know any geometry; the most important things to learn by far are the trig identities, and some other little things like the pythag theorem, radians, and simple stuff about circles, along with a basic understanding of coordinates. At this point I'd imagine you can start to learn calculus; the meaning of differentiation and how to differentiate any function you can write; various applications of differentiation. Then learn about definite integration and Riemann sums, and learn how it relates to anti differentiation. Then there's a whole host of integration techniques.

At this point you should have a good understanding of the basics, and where to go. You should also get to grips with vectors at some point; scalar and vector products; the equations of planes, etc. You'll find the stuff you can potentially learn increases very quickly due to the high degree of interrelation; for instance, a very fundamental and basic function is the exponential, but you need the basics of calculus before you can understand it.

Other places to go: differential equations; matrices; Taylor series; complex numbers; induction; conic sections; multivariable calculus.