It is almost impossible to fix a sauce that has had too much salt added to it; however, the cook could dilute the sauce or add other ingredients that may overpower the salt such as lemon juice, wine or vinegar, although this may not suit a tomato sauce. The addition of starches, such as noodles or rice, may absorb some of the excess salty flavor. The noodles or rice can then be removed prior to serving.
If the sauce is diluted, other flavors will be reduced as well, so the cook should be prepared to season the sauce with more ingredients. A thick and creamy sauce will be tough to dilute, so this tip is best used on a broth type of sauce.
To avoid too much salt in the future, the cook should add salt gradually and taste it regularly. A soup or other sauce will become saltier as it simmers, so tasting the sauce after the salt has just been added may not give an accurate flavor. Cooking is not an exact science, so one of the best things a cook can do is taste, then adjust. Repeating this frequently throughout cooking process is one of the best ways to ensure that the food will not be too salty when serving.