I'm pretty sure the common advice is not to pull it back, apparently that can do damage pulling it back before it's ready.
Just keeping the area really clean by wiping well at nappy changes, and if there's a poop explosion and you aren't convinced you got the tip of the penis clean enough, then maybe try a bath.

You will notice if it looks infected (neither of mine have had foreskin infections so far), and I suppose then you could visit a doctor. As for when we can pull it back, I always thought that it just came away on its own...