1. Cook the spaghetti about 2-3 minutes less than recommended
2. While cooking the spaghetti, heat your sauce until it's simmering, don't boil it.
3. When the spaghetti is al dente, scoop our a cup or more of the pasta water, drain the remaining water
4. Pour a cup of the pasta water into the sauce to thin slightly.
5. Put the spaghetti into the hot sauce. Stir with tongs about 1-2 minutes more
6. Add two tablespoons of olive oil or butter
7. Crank the heat and stir the pasta constantly until the butter emulsifies the sauce & the remaining pasta water.
8. Remove from heat, let cool slightly, add a small handful of Parmesan and give it one last swirl
9. Plate the spaghetti, drizzle with a little more olive oil, sprinkle with fresh herbs, basil, parsley, etc.

It's really not that much more work but once you let the pasta water and the butter or oil (oil is more traditional, personally I like butter) do their thing you'll never do it any other way. By the way, my friend Tony isn't shy about using canned pasta sauce when he's in a hurry.