Since Neapolitan pizzas must be small to bake up properly, you’ll likely wind up making several of them in a row for you and any guests you might have. This isn’t a big deal since they cook up so quickly, even in a home oven. The big things are the dough (which I’ll show you a bit later on) and the tomatoes.
As previously mentioned, Neapolitan pizzas have no sauce on them (unless they’re “marinara” pizzas, in which case the only ingredient they have on them is sauce). They simply have tomatoes. Usually canned. Buy whole canned tomatoes, which you can prepare up to a day or two ahead of time. Simply strain the tomatoes of their liquid, then under running water open them up and rinse out the seeds. Once that’s done let them sit in a colander for a few minutes to drain any residual moisture (pressing them with the palm of your hand to help the process along), then put them in a small bowl and chop them up a bit using a stick blender. Alternately you can use a food processor, just don’t work them too hard. You want a slightly chunky mixture, not a liquid one, which will soak into your crust and create a wet finished product (it’s the nature of a Neapolitan pizza to be a little wet, but you don’t want it sopping). That’s it! You don’t want to cook them at all since they’ll cook on the pizza. You may add a little salt if you’d like, but I recommend trying it without. As I said, Neapolitan pizza is an austere experience, you may decide you like it the way the Italians do: simple in the extreme.
Cheese-wise, you want nothing more than thin (as thin as you can slice them) slices of fresh mozzarella on hand. It pays to do the slicing half an hour or so ahead of time, ditto for the picking of basil leaves and the prep for any other ingredients you might want to put on. The only thing I recommend cooking ahead of time is sausage if you’re using it, and then just until it isn’t pink, since it will brown in the oven.