Look around the garden and mark down the plants you need to replicate and extend. These could be your favorites from the garden. Leave out the hybrid plants because although they do have desired traits, their seeds are usually infertile.
There are specific timings for each plant to gather the seed. For some you can gather the seeds after plucking them when they are ripe and saving the seeds while you use the rest parts. For others, you have to let them get dry and mature till you can gather the seeds. This might bare you from using them this season. Like if you want to save cucumber seeds, you will have to let it dry first.
There are two types of seed and drying process for each is different. For those seeds which are scraped off easily and not covered in any pulp, spread them on a tray and leave them in the sun to dry. Give them a week in an airy place to dry fully.
For those covered in pulp, soak them in water after taking them out. The water will rinse the remaining pulp. It also helps you select bad seeds from good ones. The good ones will sink to the bottom while the bad ones will float. Remove the good ones and dry them on a glass tray like the seeds above.
After the seeds have dried well, its time to s tore them for the season. Bring out the containers that you collected for them. Pour in the seeds and label the containers. You can also store them in envelopes.