When boiling potatoes, your best bet is to salt your pot of water before you toss them in. Adding salt from the beginning is your only chance to penetrate the potatoes with flavor.
A good rule of thumb is to use a teaspoon of salt for every pound of potatoes you're boiling. You can always check the salt level of the potatoes once they're boiled.
Taste some of the boiled potatoes to see if they're too salty or not salty enough. The next time you boil potatoes, you can adjust the quantity of salt accordingly.