Please Help Me Get My Baby To Nap!

Susan
Once he started sleeping through the night his naps became more erratic and shorter. There are so many days where if he doesn't fall asleep in the car while I'm out, he won't nap more than 30 mins at all, even on me. I know naps are so important for his health and development so I keep trying to make it happen for him but I feel like such a failure. 
How do you get your baby to nap? Did you start following a baby schedule? How do you start one? If baby won't nap at the scheduled time, what do you do then?! Please help!