This is what I posted somewhere else. You may find it useful

Matrices is a must, by far the easiest. The rest then depends on whether you prefer logic or formulas to solve problems.
If you like to use formulas, then consider business maths, number patterns and possibly geometry and trigonometry, especially if you like working with diagrams.
If you like semi logical problems, then graphs and relations is good, however requires a solid understanding of interpreting and constructing linear graphs and equations.
If you are 100% logic type person and enjoy working with diagrams then you will love networks, however if you love your formulas and like being able to check your answers algebraically, then you will hate networks and I don't recommend you do it, no matter how easy some people will tell you it is