Basic starter troubleshooting.
Does your car click when you try to start it? Click several times before it finally starts? Check the following:
1) Check the battery posts for corrosion, make sure they are tight and clean. Get the battery tested if its an old battery.
2) Check your grounds. One behind the battery, one that bolts to the transmission to one of the starter bolts, one on top of the intake manifold. Make sure they are connected and not corroded.
3) Get your starter tested. If you remove the starter and take it to AutoZone or Advanced Auto and they will be able to test it. Or before taking the starter out, you might want to pull off the wire going to the starter solenoid, and hook up a little alligator clip to the terminal on the solenoid, and touch the other end to the +12v terminal on the battery. If it doesn't crank right away, the problem is with your starter. If it tests bad, replace it, if it tests good then onto 4).
4) If your starter is good, your grounds are good, battery is good, theres not much else to check besides the ignition switch on the steering column or the starter relay in the right fender well.