Test for texture.
Once the water comes to a boil, add your pasta. The type of noodle doesn't really matter, but generally, when it comes to long shapes, go with thin strands for lighter sauces and thick ones to stand up to heavier sauces; use short pasta with chunky sauces – curvy shapes like fusilli or orecchiette, especially, will pick up the good bits.
Stir a few times during the first minute. The starch gets sticky when it heats up, so stirring keeps the pasta from clumping – no oil necessary. Nor is it recommended – the better for the sauce to cling to, not slip off, each noodle. After two-thirds of the suggested cooking time, bite into a piece to test for doneness. Keep doing that once a minute, until the pasta has no white in the middle but is firm and just a little chewy – this is the al dente ("to the tooth" in Italian) texture you're looking for. As soon as you get it, turn off the heat, save a cup of the cooking water to use later, and drain. Don't run the pasta under cold water; it'll wash off all the salty starches that'll enhance your sauce later.