It depends on the recipe, what you're cooking, and how much you've over salted, but often you can salvage the recipe if you've added too much salt. Sometimes adding a bit of an acid, such as lemon juice or vinegar, will counteract the saltiness. If you're cooking a slow-cooked dish, such as a stew or soup, add a peeled, halved, raw potato to the dish and it should absorb some of the salt.