When he wakes at night I keep things dark and quiet, pick him up and he usually goes straight back to sleep. Some nights I give him a bottle if he's been awake over an hour. It's not a magic cure, although he'll usually go down about half an hour later
The advice I had, which worked, was not to pick them up and not to give a bottle - because those reward your child for being awake in the night.
Pat, reassure, say boring same phrase every time, leave.
5 minutes later
Pat, reassure, say boring same phrase every time, leave.
5 minutes later
Pat, reassure, say boring same phrase every time, leave.
5 minutes later
Etc
We did this for several weeks, extending the 5 minutes to 10, then 15, etc.
Having someone else give us the instructions meant that we weren't changing our minds in the middle of the night - we just did exactly what we were told.
It did work eventually.