Oxygen, heat, and light are the enemies of your hops. Store them in the freezer(ice cold and dark) preferable under vacuum, and they'll last a year or more. Vacuum bags are good, as are mason jars which can be vacuum sealed with a jar adapter and a brake pump($20)
If we're just talking about a couple ounces, if they're already in a Mylar bag, toss them straight in the freezer. If they aren't, just put them in a double locked zip lock bag.