There's a few things you should know.
1) You'll have to pass a physical fitness exam, so get in shape, or stay in shape, depending on if you're in shape already or not.
2) You'll have to pass a civil service exam, so get to know the difference between right and wrong if you don't know it already.
3) They'll do a background check, so if you have anything outstanding, don't waste your time, otherwise, just stay out of trouble.
4) You'll have to pass a lie detector test, so get used to telling the truth if you don't do so already.
5) You'll have to pass a drug test, so anything you don't have a prescription for, stop taking.
6) This one's just more of a warning to prepare you for the future. While in training, at some point you have to get sprayed in the face with pepper spray. This is so that all police officers know what it feels like before doing it to others (prevents a law suit), and it helps you to build up a small immunity to it (it will still sting like no tomorrow, but just a little less) incase someone gets your own pepper spray and sprays you. Just wanted to warn you about that.
Anyways, so if you go to your local police station, they can direct you in which forms to fill out and which academy they'll ship you off to and for how long.