I recently had the pleasure of attending two local seed saving workshops in which the lecturers gave basic information on how to do seed saving. How seed is saved, depends on what type of seed is being saved, as certain seeds require special handling and processes. But, in general, the concepts of saving seeds for edible plants (i.e., vegetable seeds), are consistent across the board and discussed below.
Although you may want to harvest the ripest, choicest, best-looking vegetables for your own consumption, if your goal is to save seeds, you should reserve the best of your harvest for that purpose.
After you have selected your vegetables, depending on what type of vegetable you are handling, you will need to extract the seed, making sure that it is a good size. no deformities, and that there are no signs of disease or pest infestation. You will need a way to clean off any debris attached to your seeds and dry your seeds thoroughly; otherwise, mold may develop, rendering your seeds unusable. You may dry seeds by placing them on a screen in a dry, protected area. Even setting seeds in an oven on low heat (approximately 100 degrees Fahrenheit) may do.
Frequently, some amount of debris will be attached or mixed in with the dried seeds. A simple mesh screen attached to a wooden frame will often do the trick. You place the seed and debris on the screen and shake it over a box or a large container or surface, much the way you would pan for gold, and depending on the size of the seed or debris, one or the other will be left on the screen. You may have to make several passes to clean your seed sufficiently for storage.
At one workshop I attended, I observed a unique method, where the lecturer took a handful of seeds which was mixed in with debris, tossed the seeds in the air over a box, and used a hairdryer to separate the “wheat from the chaff.”
After the seeds have been dried and separated from the debris, they are ready to be stored. They can be placed in small paper envelopes, labeled, and set in the freezer. Seeds are alive and respire; the freezer will minimize the rate of respiration and will keep seeds fresher, longer (although how long seeds keep, depends on the variety of seed).
You can find a lot more information about saving specific seeds either in books or on-line. Also, you may consider participating in seed swaps, which occur all over the Bay Area.