Use a large pot with plenty of water
Bring the water to a full rolling boil before adding spaghetti
Stir immediately after adding the pasta
Stir occasionally while cooking
Add salt to the boiling water
Do not overcook the spaghetti
Drain the pasta as soon as it is done
Toss with sauce right away
If needed, add a little pasta water or sauce to loosen it
Do not rinse unless you are making a cold pasta dish