Use a Dutch oven or a stockpot to allow room for the pasta to move freely in the boiling water, and it will cook evenly.
Use 4 to 6 quarts of water to cook spaghetti and other "long" pastas or to cook 1 pound of shaped pasta.
A bundle of long pasta about the diameter of a quarter weighs 4 ounces and will yield 2 cups of cooked pasta.
It isn't necessary to add salt or oil to the water. Omit them when preparing pasta to avoid adding sodium and fat. However, you can add lemon juice to the water for subtle flavor.
Bring the water to a rolling boil, and add the pasta gradually so the water will continue to boil. Once all the pasta has been added, stir and begin timing. Stir often -- you can't stir too much!