Instead of a frozen pizza, we purchase just the dough from the bakery section of our local supermarket. Usually this is frozen, if not you must use it that day. We thaw it in a covered bowl for about six hours.

Sprinkle a small amount of corn meal on the stone (to keep the pizza from sticking) and put it in the oven to preheat.

While it is preheating, spread out and shape the dough on a thin cookie sheet or waxed paper. Do this by hand, not with a rolling pin, and again spread a little corn meal to make it easy to slide. Once the pie is shaped, brush on a SMALL amount of olive oil in a few places around the edges and the center. This seems to give the crust a bit of crispness. Do NOT put any oil on the stone, or on the bottom of the pie. Using the bottom of the spoon or ladle spread out whatever sauce you like. We tend to spread it thinner rather than thicker as this gives it a chance to bubble up. Sometimes we make our own, but mostly we just use one of the prepared pasta or pesto sauces. We like the "Classico" brand. Put on the toppings: pepperoni, roasted peppers, green peppers, olives, mushrooms, onions, fresh basil, oregano, hot pepper, whatever you have on hand or are in the mood for. We tend not to use mozzarella, but rather feta, or gorgonzola, or ricotta, or most often, a goodly amount of Parmigiano.

Slide the pie onto the preheated stone, bake for about 12-15 minutes, checking the bottom to see when it is properly done. We use that thin cookie sheet for a "pizza paddle." This may seem like a bit more work than just buying a prepared frozen pizza, but not really, and you can come up with some really innovative pies.

PS: When we used convection bake in our new oven, the pizza came out overdone on the top, and under done on the bottom. Have since found out that convection does not work well for pizza done on a stone.

As svwillow suggested....don't forget to preheat the stone. Put it in your oven and turn the oven to 450 and let it preheat at least 20 minutes...40 is better, then put your pizza on that blazing hot stone.
You'll see!
Linda C

You can't really cook frozen pizza properly on a stone.

For a stone to do it's job correctly, it has to be preheated for 30 minutes MINIMUM (when baking my artisan breads, I preheat my oven/stone for an hour). BUT you shouldn't ever put a frozen pizza on a hot stone--the stone will crack because of the temperature differential. And if you put a frozen pizza on a room temperature stone, then try to bake it, the stone won't get nearly hot enough to crisp up the bottom crust in the time it will take for the top of the pizza to get done.

The answer is, make sure your stone is thoroughly preheated, and then bake a room temperature (homemade) pizza on it.

You may find this old sermon of mine useful. Soggy pizza is caused by oven temp selection too low or oven not left on preheat long enough. Oh yes, too much sauce and other toppings will give it the soggies too. Since you were doing ok before the pizza stone showed up, the culprit is lack of heat.

A few hints about pizza stones:
Keep a scrubpad for use only with the stone. Clean the baking surface of the stone with it and running water only. Never use any kind of soap. Don't soak the stone.

The first few pizzas using the stone will probably have an odd tasting dry crust. To avoid this "bake" the stone a few times on its own. You can season and bake the stone with a VERY light coating of veg oil to lessen this effect and help start the creation of a nonstick coating. Once pizza production starts the seasoning can usually stop.

Pizza stones of the $10 type are usually made from compressed sand and are really rugged. I've placed frozen pizzas onto stones at 430F and haven't lost one yet. The secret seems to be get it down fast, flat, and centered to lessen thermal shock.

My recipe for a frozen Kraft Delicio. I like them in a pinch because they don't overdo the sauce and toppings so the bread has a chance to become something other than a soggy mess. Also like to pop off the frozen pepperoni and put it back 5 minutes before the finish :

Preheat ordinary oven half hour or so 25 to 40 degrees above directions given on pizza box with stone on next to lowest or lowest rack. When ready, quickly open oven, push the frozen pizza so its "front" edge goes nearly to the back edge of the stone and quickly drop it in place it so it is centered, close oven. When the crust and cheese start to darken put the pepperoni back on top and close oven. I like to have it in a ring on a paper plate and quickly upend it so it all falls in a circle about halfway between the center and crust. Leaving the center bare helps the bread in the center to finish rising. If necessary, I use silicone turners to ensure the pizza isn't stuck to the stone when it's time to remove it.

Leftover or even made ahead pizza slices quickly reheated in the microwave produce a soft breadlike crust which some folks prefer to the fresh from the oven crustiness.

Your results will be unique to your conditions of course. A pizza stone is a very handy item to have around. Good luck!

Or buy a cast iron pizza pan instead....