Just last week, I gathered Swiss Chard seeds (December!). Always be on the look out for seeds!
Every year I have a seed gathering and saving project. I plant heirloom seeds or plants and gather the seeds. (Hybrid seeds don't continue to produce the same fruit, and eventually will not produce any fruit. A good example is of how hybrids work is a hybrid tomato plant or seeds that sends up volunteer plants the next season, they are small, cherry like tomatoes.)
I air dry them on a paper towel or wax paper. A good place to dry is on a shelf or table top where they can be seen and they won't be forgotten.
When the seeds are nice and dry, I put them in a recycled container. It's best to put the seeds in a glass or plastic container instead of paper. In the past, I've had mice raid my paper containers and steal my seeds. Always date and label every container with the contents. Even though it might seem easy to remember what type of seed and the year they are saved, as time goes by, identification may be more challenging then imagined. Always label!
It's nice to have seeds on hand when planting season rolls around. Having seeds stored gives a feeling of preparedness. If extra seeds are saved, it's fun to be generous with them.
Some years I have a good harvest of seeds and take them to a seed exchange or share them with friends. A seed exchange is really fun, normally they don't cost anything, it's just people like me who have extra seeds and share them.
Seeds age and depending on how cool, air tight and dry they are stored, will determine how long they will be viable. As seeds age, they are less likely to sprout. Use seeds the next planting season if you can, but if you have left over seeds, there's no harm in saving them, if they are stored well, they may sprout the next year, and even the next. There are stories of seeds being found in the pyramids in Egypt that are 1,000 years old and they sprout!
When my mother passed away, she had quite a collection of seeds, many that she had gatherd and dried. I enjoyed going through her seeds. Seeds have a special meaning to me, they represent life.