Patience. Babies can adapt just about any schedule but you have to be very mthodical and very persistant. If you want a baby to go to sleep at a certain time, keep them awake for as long as possible before that time. But more importantly put them down for that nap at the same time every day. By the clock. Eventually they will adapt and get the idea. It may take a while. Be persitent.
Routine. Most babies are ready to take a morning nap about 3 hours after they wake up. Plan your routine around this. Develop a nap routine, and put your baby in his/her crib awake and allow him to soothe himself to sleep.
How old? Babies give up naps at different ages. Most babies under 6 months take several naps a day. If the baby is sleeping all night, I wouldn't worry about a morning nap. If he's not sleeping all night, less sleep during the day will lead to more sleep at night.