After a while you will probably learn his potty schedule. Here's what I do with a young puppy.
Take him out first thing in the am, about 10-15 min after each meal, after naps, and after a lot of exercise/play time. You'll probably end up taking him out every 1-2 hours during the day. Supervise him constantly and crate him if you can't watch him.
It sounds like you're probably doing all or many of these things already.
As far as cues he needs to go out, look for sniffing, circling, whining, restlessness, or heading towards the door. You'll learn to recognize his signals the longer you've had him. And make sure you clean up any messes with an enzematic cleaner so he's not attracted back to the same spot.