There are expiration dates on your packages. They should be stamped "Packed for 2013" or whatever year the seeds were sold at retail. Seeds that are only a year or so old and whose packets are still unopened generally germinate very well.
If they are older than 5 years and the packs were opened or the seeds were stored where the temp and the humidity add up to more than 100 when combined its a no-grow.
Your garage or basement is a great place to store seeds, because they are typically dark, cool and dry. The temperature remains pretty constant. Most seeds stay viable longer if stored at a constant temperature of 40 degrees or lower.
There is a 10-day germination test you can do to see if they have any growing power whatsoever.
Place some sample seeds inside moist paper towels and slide the towels into a plastic bag. Mark the type of seeds on the front, but don't seal the bag. Let them sit out in the warmest room of your house and check them at Day 5 and every day thereafter. Viable seeds should sprout by Day 10. If they don't, or if less than a third make it, get fresh seed.
If you have a flower or fruit that bloomed just perfectly and you are hoping the seeds from the plant will get you a repeat, make sure the seeds are totally dry before you store them. Put them in a single layer on a paper towel on the counter so they can dry out. You can then put them in an envelope, date it and label it and drop them in a jar. You do need to shut it tight so no air gets in.
Now next time you're ready to plant your seeds are waiting and ready to grow.