the above is great advice.

dont forget there are other ways of making your slave target things and kill. one is by using targettarget and the other by using focustarget with your main as the focus.
macros will be written differently, and gameplay will be done slightly differently. but it just dpeends in your preference. try the above setup, but also try the targettarget setup and the focustarget setup. also remember you have more abilities than just fireball and frostbolt. so you'll have to figure out how to use them for both your characters. if you wanna know my setup (my mages are only 20something though) i can give you a quick start setup with minimal addons, configuraitons, etc.