make sure they are completely dry, put in ziploc bags in a jar or something. I keep mine in jewelry-sized ziploc bags and the jar keeps mice and stuff out. Some people freeze them for longer storage. Also, some seeds need to be stratified (need a period of cold, i.e. winter) before they can germinate. Google the flowers you are saving seeds from and see what you can find about saving the seeds, and if they need to be stratified.