Whether you bake or grill, the trick is for the toppings and the dough to cook in sync. Keep the following in mind.

• Cook meat and veggies before topping: Pizza doesn't bake long enough for most raw meat and vegetables to become tender. Better to use slices or crumbles than chunks.
• Pick the right time to add toppings to oven-baked pizzas; Delicate ingredients may overcook if left in the oven for the full baking time. Sometimes better to add them half way through the cooking.
• If you're grilling your pizza, cover the grill after adding moist toppings e.g. tomatoes or cheese or they may not cook through.
• When grilling pizza don't overload with toppings as you risk losing part. Use the oven to bake if you intend to "load-up" with toppings.

Thanks to How to Cook Everything by Mark Bittman