Steve,
I’d print out and tape to each order a special, “good for the next seven days only!” coupon on bright paper. Use a 5-10% higher than normal food cost but bundle a couple pizzas and maybe some sides with it. The coupon should thank them for their loyalty, etc. Write the date on the coupon when you send it out.
This is a basically free way to gain repeats.
I would also recommend a give-away promotion in exchange for people programming your number into their cell-phone.
If you’re going to give it a go, advertising is everything. You’re not competing with 35 pizza places, you’re competing with their mailers, their commercials, their magnets, etc. Quality is everything to us, but to the consumer, it’s basically whoever comes to mind first when they decide they want pizza.