Dry, not too hot(like in an attic, they'll cook)not too cold (like a freezer). I have mine in the paper envelopes they came in, other mail type envelopes, little ziplock bags, film canisters, in a cardboard box.
The yard long beans i planted this year are 2 or 3 year old
seeds, spinach about 5 years old, tomatoes 3-4 years old, morning glories 4 years. Thay all sprouted fine.