Have him spend ample time in positions that you will find useful when you want him to service you. It will help put him in the right frame of mind and he will become more useful to you.

Make him avoid certain postures throughout the day that you feel lessen his submissiveness or keep postures that increase it. For example, for a female sub, keeping legs apart and uncrossed. I imagine you can think of appropriate equivalents for a male sub. Each failure to remember garners punishment or discipline.

These two things work nicely because it lets you exert your control both in person and remotely.