Despite what you may have heard, adding oil to the water does nothing. A pinch of salt lends a little flavor—but again, does nothing to prevent clumping. The only way to prevent pasta from sticking as it cooks is to be sure you have plenty of vigorously boiling water. When you think about the fact that pasta expands to about three times its size when it cooks, you can see why if you try to boil one cup of pasta in two cups of water, it's going to all stick together. Now picture that same one cup of dry penne jumping around in eight cups of boiling water—and you can just as easily see why it won't clump.
Practice your skills with our collection of pasta recipes.