What time are you putting him down, also let him be active like 30 min before wind down time. Give him a bath, shut the lights down and if your still up let him listen to the Baby programs while he drinks his goodnight bottle or whatever. That way he will slip into his sleep. I also used to put like one of my shirts in the crib with my boys. Sometimes if they smell you they will think they are with you and sleep longer. Weird but I swear it worked
If my son has more than a 2 hour nap in a day he sleeps terribly at night. We also have a routine so dinner, play, bath, play a little more and then bottle & bed and he'd sleep until 8:30+ if I didn't have to get him up so I can go to work.