The normal way is to add a couple of Snails and Hermit Crabs first, wait a few days to see if nothing's wrong with your water/setup. If the snails are doing fine after a few days, you can then add more snails/crabs. After a few days, add a shrimp, if he's doing fine, then add fish.
Of course this is the cautious way of doing it. You may decide to add the shrimp sooner, with the second batch of cleaners (ie. snails and crabs).
I have 10 snails and 2 crabs in my 33g, with a blood shrimp. The tank is almost two months old and is now cycled. I'm ready to add a couple of Clowns...