2 large tomatoes, the best you can find
Chiffonade fresh sweet basil leaves
High quality EVOO
Salt, pepper to taste
I usually will slice my tomates either in rounds or in quarters, salt them, and let them drain some of the water, concentrating the flavor. I don't typically seed them unless the juice is over the top. Cut your cheese however you want (I happened to do little sticks this time), drizzle with balsamic vinegar and EV olive oil (something STRONG). Finish with basil, salt and pepper. Some people don't like pepper on tomatoes, but I do. I also go a little heavy on salt, but it's so complimentary to tomatoes, that I don't mind.
A more classic way to do it is to have round tomato slices, full basil leaves, and round cheese slices stacked on top of each other. The colors are representative of the Italian flag (Margherita pizza?). Then put your finishing touches on it. Either way, it can't miss!