Every gardener has a different way of storing seeds. Some like plastic baggies others like paper envelopes. Personally, I like the paper envelopes since they don’t retain as much moisture and keep the possibility of mold to a minimum. Look on gardenhere.org for patterns for large and small seeds envelopes or find ways to make your own using mail envelopes, coffee filters, etc.
Always, always, always label your seeds. Sometimes mystery seeds are fun, but you really do need to know what they are so you can plant them in the right place at the right time come next spring. It might also be a good idea to label your paper towels or plates you use to dry seeds so you know what they are when your pack them.
Still you need to find a place out of direct light, high temperatures and high humidity to store your seeds. Since the majority of us don’t have climate controlled rooms especially for seed storage we have to do the best we can to keep them from going bad. A few options would be the refrigerator, a closet, or an attached garage (in the winter). Shoeboxes, plastic tubs with lids, old wet wipes container, and file cabinets are all viable places to keep your seeds. One tip I found interesting to keep moisture to a minimum is to put the silica gel packets you get from clothing and shoe boxes in the boxes or drawers where the seeds are stored.
With the passing of time seeds lose their ability to germinate properly. The more care we take to store them properly, the longer they will last.