You have to have a good grasp of math. You will use it everyday. Everything will be calculated out on the computer, but you still have to be able to work out basic equations.
Now, you aren't going to be doing calc, geometry, or statistics during work. You will have do be able to find out drip rates and drug calculations in school. There will be times at work when you have to figure out how many milligrams per kilogram to give someone, and then calculate how many milliliters to pull out of a standard bottle. When you give a bolus of medication, you have to know how many mg per kilo to order (pharmacy will do most of it, but you still need to know it). Sometimes, pharmacy will just enter the bottle in the pyxis and you have to mix it (which is why you have to know it).
There are other areas besides meds that you have to use math. You have to be able to calculate blood pressure changes, intracranial ranges, pulse rates, IV fluid rate, etc. If you move on to a BSN, you have to calculate monetary equations, process improvements, and incorporate statistical information for managerial positions.
The good thing is you will learn all of this in school. But, make sure you do what you need to improve your math skills. They won't let you through if you can't pass your drug calculation test.
The requirements for school are mainly pre-regs (which vary). A&P I and/or II, english comp, math, psychology, maybe sociology, maybe micro, an essay, maybe some volunteer work. Check with the school you pick and see what the requirements are.