If you are not familiar with the nitrogen cycle, read up on wetweb
http://www.wetwebmedia.com/marine/index.htm

You should be able to watch for a peak in Ammonia, then Nitrite, Then Nitrate. Once you have seen the spikes, and Amm & Nitrite remain zero (or very close) and you can maintain low nitrate with water changes, then add hermits. Blue leg hermits are probably the best at algae control, but reds and zebras do ok too. Depending on your system, this initial cycle could take 30-90 days, and the tank could get rather overgrown with algae during the cycle. A week or two after the hermits, add various snails: Astreas, nassarius, and cerith.

How long has the tank been setup? What size? What type of filtration?