I have one of those hand held screen strainers.I put my seeds that I want to save in one and hold under the faucet and swirl with my finger to rinse off any gunk.Then I dump out onto a paper plate to dry. Spread around to dry better. Then once dry I scrape off plate or paper towel and save in small container and label.
Depending on the size of your screen, bell peppers, squash, tomatoes, watemelon, anything you get out of a fruit, melon, or any seed that is "wet" when you get it. Some things like okra, beans, marigolds or zinnias should be dry when you collect the seeds, but this method works for about any seed that is not "dry" when you collect it.