I’m a minimalist when it comes to pasta.
I don’t mind most jarred sauces. They get a bad rep, but there are some good ones and some mediocre ones that can be brought up to code.
Chopped tomatoes are a good start. I usually used canned just because I don’t like the flavor of raw tomatos and fresh ones seem to give the sauce that same flavor.
It’s always good to use as many fresh herbs as you can, but they can be costly if you have to buy them. (depends on your local and time of year). If you’re a gardener, try growing some basil and oregeno yourself. There’s nothing like going out into the garden, picking your spices and tossing them right in.
A good italian sausage will be an improvement over ground beef. In fact, try using it in any recipe that contains ground beef (except hamburgers and meatloaf) it even makes Hamburger Helper edible.
Beyond that, I only add onions and green pepper, I know some people who throw everything but the kitchen sink in, but that’s not for me.