When you add the broth and get the soup simmering, the soup will at first taste under-salted. Remember that the soup is going to reduce a little as it simmers so resist the temptation to add more salt at this point.
A few minutes before you're ready to take the soup off the heat, taste it again and add more salt as needed. With my soups, I find that another teaspoon or so is usually needed to brighten the flavors and bring the soup together. Now when you serve the soup, the seasonings will be just right.
If your soup still ends up tasting a little salty, first try adding a few more cups of broth or water. This will thin out your soup - and the salt. You can eat it like this, or you can add a potato or two to absorb some of the extra liquid (and, yes, its salt!). A cup of rice or some pasta will accomplish the same end.
Any other tricks for avoiding an over-salted soup or adjusting for it post-facto?
Related: Quick Tip: Make Cheese Rind Stock!