Saving your own seed stock? You are to be commended. It is prudent, cost effective, fun and possibly even a (minor) source of income. Let's take a look a tomato seeds. If you looked over the posts on saving cucumber seeds (and if you didn't, you can find those posts HERE, HERE, and HERE) then you already know how to save tomato seeds.
There is one important difference, there is no benefit to be gained by waiting for them to fall apart from decomposition. a ripe or slightly overripe tomato is a fine seed source. You can even pick those half eaten by chipmunks or which have cracked from a sudden growth spurts.
Their seeds, saving those located in fat little chipmunk tummies, are perfectly acceptable.
Simply squeeze out the glop and follow the cucumber seed instructions.
Only use open pollinated varieties! If you are not sure what your "Giant Martian Hypersteak Tomato" is, exactly, just look it up in on line seed catalogs. If it is open pollinated, bravo and forge ahead! If hybrid, hurl it from you with righteous disdain. (Or make it into sauce)*
Now isn't that easy?
Thanks for stopping by!
*NOT "GRAVY" ITS NEVER "GRAVY!"