How can I keep my baby from waking at night or get him back to sleep quickly?

My baby wakes every night between 12:00-1:00 and 3:00-4:00. You can set your watch to this pattern. Getting him back to sleep at 12:00-1:00 is easy with a pacifier and some calming but the 3:00 hour is usally met with active alert and it's a little more difficult to put him down. Any thoughts on how to either prevent this pattern or put him back to sleep quicker?