Do not save hybrids. Do save heirlooms. Do save organic.
Not every plant’s seeds are worth keeping. Hybrid plants are developed by crossing specific parent plants. Hybrids are wonderful plants but the seed is often sterile or does not reproduce true to the parent plant. Therefore, never save the seed from hybrids. Another major problem is some plants’ flowers are open pollinated by insects, wind or people. These plants include squash, cucumbers, melon, parsley, cabbage, chard, broccoli, mustard greens, celery, spinach, cauliflower, kale, radish, beets, onion, and basil. These plants cross with others within their family. The only way to maintain the original variety is to isolate by large distances. Isolation is often impossible or impractical in a home garden.
Use silica (or silica cat litter) to prevent moisture seed spoilage.
Keep cool, and dry.
Store in paper bags or glass jars.
When using a storage area that is cool and dry year round, you may be able to keep seeds in paper bags, mesh bags, or envelopes in what is called “open storage”. Moisture and heat generated by the seed during respiration can escape through these gas permeable containers. This is also a smart tactic when you aren’t sure about the moisture content of the seed. But you will still want to take precautions to protect your seeds from pests.