I think there are 2 main ways to keep people subservient. Lets start with the more common one.
If you want to break someone, this is what you want to steer towards.
As long as you keep them scared of what could possibly happen to them, they'll behave. It's a simple concept and often very efficient. Examples that come to mind, for example, is any hostage situation. The armed villains have weapons and threaten the hostages lives - the hostages listen and do whatever the villains tell them to do, eg: get on the ground, hands on your head, etc.
Start with the initial fear, and condition it so that they're always scared, hence breaking the individuals will.
In fact, you don't have to continuously apply pain/torture techniques. You just have to do it once, bad enough that they never want to feel it again, and then remind them once in a while that they'll feel it if they don't obey.
If you're actually looking for a technique... just take one of your prisoners, put him under Chinese water torture (while hidden from the rest of the prisoners). When he breaks and goes nuts, bring him into the public and show him around to the prisoners, and don't tell them what you did to this guy. Make them use their imagination. Then, rip out his nails one by one, burn half of his body, slowly flay the other half of him with a blunt knife, and then send him to be drawn and quartered. Then go and kill his family the exact same way, in public.
(And if you really want to make it bad for them, somewhere along the flaying process start putting salt on his wounds. Literally. Don't forget to make your prisoners do the drawn and quartering of their comrade. Whip them forwards until he gets ripped apart.)
Edit: Courtesy of Jason C for reminding me of this. You can also deprive the prisoners of nourishment and make them work for it. If they don't work, they don't eat.
This is the nicer way to do it, if you don't want to break them after capturing them.
Give them something to obey for. A prize, perhaps. Any sort of incentive.
Or, give them someone to worship - an idol, maybe a lover? People will do (almost) anything for the people they love...