SeedSave is an awesome website that has information about saving seeds.  They even offer seed saving schools online.  They also have information online about how to save each different type of seed.  I have copied a sample from their Beginner seed saving page to give you an idea of the wealth of information you will find on

Bean - Phaseolus vulgaris

PLANT: Although, ideally, different varieties should be separated by 150 feet or another crop flowering at the same time, we rarely observe cross-pollination even when two varieties are grown next to each other.

FLOWER: Beans produce perfect, self-pollinating flowers. Cross pollination by insects is possible but rare as pollination occurs before the flower opens. Because the anthers are pushed up against the stigma, automatic pollination is assured when the anthers open.

SELECTION TRAITS: Most commercial breeders favor bush varieties which can be mechanically harvested and fibrous bean pods which hold up during harvest and shipment. Pole varieties are more suited to small, home gardens because they produce more beans in a smaller space. Because vines are off the ground beans are easier to pick and away from the settling cold air of unexpected frosts. Plant growth: Pole type growth, D; Bush, r. Pod edibility: Little or no fiber, r; Stringless, r .Seed color: White seeded varieties are better for canning because seed color doesn't affect canning liquid, r; Colored, D. Pod, foliage and flower color: Purple, D.

HARVEST: Allow pods to dry brown before harvesting, about six weeks after eating stage. If frost threatens, pull entire plant, root first, and hang in cool, dry location until pods are brown.

PROCESS: Small amounts of pods can be opened by hand. Flail larger amounts. Remove large chaff by hand or fork. Winnow remaining particles.