Anyway, the key to tomato sauce (“marinara” is something different in my book, even though most places and companies confuse the term) are the tomatoes. While that may be obvious, using canned tomatoes may not be.
Fresher is not always better, especially when it comes to tomatoes. Preparing fresh tomatoes to use in sauce takes an awful long time, a lot of work, and even then, will usually not come together as well as the canned kind.
I have a picture of Rosa tomatoes here, but you can use any kind, as long they’re Italian. I know, it’s snobby, but the Italian ones really are the best.
The tomatoes are usually packed in puree, and should come with basil. Make sure they do not have tomato paste (Death to tomato paste!) or are Italian style (meaning they are probably from New Jersey, not Italy: actually two different places, as opposed to what cable TV leads you to believe).
On a side note, my friend Lou maintains that the onions are dispensable, Sicilian addition. I can’t bring myself to try it another way.