There are several excellent books on the subject, none of which I can recall the titles of offhand
but which your library may have or may be able to get via interlibrary loan.
Also google and wikipedia are your friend
In general, tomatoes you may (or may not) get poor germination unless you pick a kinda rotten one, or use a fresh fully-ripe one and squish it to ferment/mold in water for a coupla days, then rinse off the gooey bits and save clean seeds. Practically anything else, though, you just get the seed, rinse egregious gooey bits off it, let it air dry, then store somewhere cool/cold and dry.
Most people keep 'em in labelled film cans or pill vials or tiny manila envelopes, or even ziploc baggies, in a sealed box somewhere that stays cool. The little silica-gel dessicant packets you get in boxes of shoes and binoculars and such when you buy 'em can be useful for promoting dryness.
Good luck and have fun,
Pat