Start with good tomatoes. There's no point in trying this with mediocre tomatoes. Buy enough to feed however many people you're going to feed. Set a pot of water in the stove to boil. Coarsely chop the tomatoes, place in a colander and sprinkle with a small amount of salt. Allow to drain. When the water comes to a boil, drop spaghetti, I use whole wheat, about 2 ounces per person in and allow to cook about 8 minutes. While the spaghetti cooks, chop garlic, up to 1/2 clove per person depending on your tolerance for garlic, and fresh basil.
Warm a serving bowl with a few ladle-fuls of cooking water, then drain and wipe dry. Toss the tomatoes, garlic, and basil into the bowl along with a pinch of crushed red pepper and some freshly ground black pepper. When the spaghetti is done cooking, drain and add to the tomatoes. Toss and then add a splash of really good olive oil. Serve, and try not to fight over the last few pieces of tomatoes that are left in the bottom of the bowl.