You can use San Marzano tomatoes from Italy (such as Cento(R) brand) instead of plum tomatoes, if preferred. If you can find imported dried oregano from Italy, it will make a difference.
Some let tomato sauce simmer 'for hours,' but I haven't found that a longer cooking period increases flavor--what it does do is turn tomato sauce into a thick gravy, which isn't very appealing.
I like to process using a food mill over the sink so I don't make a mess. A food mill yields a great consistency for tomato sauce, and opens up the flavor of all ingredients. You can also use a food processor or blender, if preferred.
You can simmer the sauce covered for a thicker consistency.