Dried herbs and spices deteriorate faster when exposed to heat, light and moisture.  The best storage temperature for herbs and spices is one that is fairly constant and below 70 degrees, if possible.  Try to stock them away from the furnace, range and heat of the sun.  If you store them in the freezer or refrigerator, be sure to return them right after use to prevent condensation or even mold.  

An ideal storage system would keep herbs cool, dry and dark.  Amber glass jars with airtight lids are ideal.  You can cover the jars with large opaque labels or even drape a cloth over them when not in use.  Treat them properly and your dried herbs and spices will last longer.

How can you tell if your seasonings are past their prime?  The shelf life of each herb and spice is different but all of them age, even under prime conditions.  Check them to see if they look fresh (not faded) and are distinctly aromatic.  Replace them as soon as you detect any deterioration.  Incidentally, whole spices last longer on the shelf than ground spices.  The shelf life also varies by the part of the plant used in the spice.  Here are some guidelines:

Leaves - 6 months
Seeds and barks - 6 months
Roots - 1 year
Teas - 1 year