I have regulars who've been seeing me for 4-5 years and who keep coming back, and I don't do anything complicated, wierd or wonderful. Some guys like to shop around, others like the same thing. Trick is keeping up your standards and providing a good, reliable service. I also try to switch around outfits and also buy in new lingerie and dresses specifically with particular clients in mind. Mixing up the order in which you do things a little and some guys will make their own suggestions.
Sometimes I've offered a slightly lower rate for regulars, especially around the time of a rate increase. Other's prefer extra time/overrun instead. Many appreciate this, quite a few actually insist on paying the new rate and some have tipped me more especially if we've overrun or they feel we've had a particularly good session. Like the person who posted above I worked out if I was to offer a significant discount across the board then most of my business would be at the lower rate.
If someone doesn't want to see you they won't book, simple.