Mine is 4 months in a few days. We make it a routine to feed him at around 10pm, give him his pacifier, rock him for a couple minutes then put him in his own cot, lights off and he would sleep for 6 to 8 hours straight. He would wake up 2 or 3 times (sometimes more) in the middle of the night (eyes closed) searching for his pacifier but he would fall back to sleep when we put it back into his mouth.
We feed our little one formula so we have to follow the 4-hr-feed schedule. Our boy usually fall into deep sleep after his 6pm (1hr+/-) feed so we would need to wake him up for his 10pm feed. We would do so by changing his nappy. Sometimes he would cry a little because we disturbed his sleep but when he smells the milk, he would be all excited and kicking. Point is we make sure he is fed at around 9 or 10pm otherwise he would be too hungry to sleep through the night.
Another thing which I think help is that he has his naps and night sleep in different places -- he naps in his highchair (those that can recline) in the living room, while he sleeps in a cot in his own bedroom. So I guess when we put him in his cot at night, his sub-conscious mind knows that it's bed time.