This depends upon the type of seed and the conditions of storage. Generally speaking, a cool dry place with consistent temperature is the best way to maintain longevity of any seed. A pamphlet released by the Oregon State Extension service also provides these general guidelines:
A more nuanced look at seed storage can be found in Steve Solomon’s book Gardening When It Counts (New Society Publishers, 2005). Solomon defines the standard storage conditions of seed as 70°F (21°C) with “enough humidity in the air that the seed stabilizes at 13 percent moisture by weight.” He notes that for every every 10°F (5°C) increase in temperature and 1 percent increase in moisture content of the seed will cut its storage life in half. Conversely, "for every 10°F (5°C) decrease in temperature, combined with a 1 percent decrease in the moisture content of that seed, the seed storage life doubles.” (pp. 132-133).