Boil the pasta, but don't drain all the water!
Boil your pasta al dente, and have a mug or a large measuring cup nearby. You'll want to scoop about a cup of the pasta water and reserve it. Remember, it's salty and starchy, and this seasoned water will help the pasta cling to its sauce and achieve a glossy, cohesive consistency. I often skip the draining altogether and let the pasta sit on the stove (off the heat) and transfer the pasta directly to the sauce using tongs.