Write, compose, commission a play, have an improv act or produce a musical revue. It's much easier to make money with dinner theater if you either own the show you're producing or it is a low cost show like a musical revue.
Keep the cast and crew small. If you have to put out a lot of money on production costs it will be much harder to make money.
Rent a performance space instead of trying to own one. It may seem like you're throwing money away, but owning a space before you can fully afford one will drag down any profits you hope to make. The best idea is to find a club that serves dinner and has the space to but on a production.
Come up with an original concept that's fun and will have mass appeal. Think of the Blue Man Group; it works because it is something different.
Publicize your dinner theater everywhere. People have to know your show is out there so you need to publicize in every avenue that is available to you. Try giving free performances at schools and universities or other places that represents your target audience.