Just be patient and learn your baby!
I'm not sure that there's any tried and true way? Baby's can sleep any lengths of time. Sometimes Charlie will crash really hard for 5 minutes, sometimes he's out for a good 6 hours without stirring. So I'm not sure about any way to get them to sleep longer, except maybe make sure there aren't too many stimulants around him like lights or music unless that's helping him sleep. You'll get to know your little one and what makes them sleepy and what doesn't. Just takes some time to learn the cues!
- needs diaper changed
- overly stimulated
And typically he is a good sleeper.. we are so blessed! :) But I agree with you.. you totally learn your baby's cues after awhile!