There is a lot of debate as to when you should add salt to your beans. I don't add salt at the beginning of the cooking process, but do add it when they are about done. Some say that if you add salt at the beginning your beans will be tough. Others say that if you wait until the end, all you will have is salty water and bland beans.
Also, if you live in an area that is considered 'high altitude,' you might want to add a 1/2 tsp of baking soda to the water while the beans are cooking. It helps to soften the beans a bit. Thanks Cheryl for the tip!