Boil pasta first, don't salt the water, there's plenty of salt in a can of tomato soup. Partially drain the pasta, you want some of the water left to dilute the canned soup, add soup, on an electric stove I turn the burner off at that point, there's plenty of heat left in the system to bring the soup up to temperature, a couple grinds of black pepper, ladle into bowls and spoon into your choice of face hole.

I do recommend using the water the pasta was boiled in rather than fully draining the pasta, adding the soup and then adding more water. The starch dissolved in the water does good things to the texture of the soup.