The Drip Method
The drip method is recommended for most saltwater fish and invertebrates because they can be more sensitive to pH, specific gravity and other water chemistry changes.
To do the drip method your going to need a bucket, a vegetable clip with a suction cup for holding the tube in the tank and a length of air pump tubing that is long enough to extend from your tank to the bucket. Place one end of the tube into the veggie clip and then place the veggie clip into your tank. Tie a knot in the tubing to regulate the amount of water flow coming out of your tank. Get the siphon going and place the other end of the tubing into the bag in the bucket. You'll want a slow drip, drip, drip going. Aim for drips every one to two seconds. If you're having troubles using the knot to regulate the drip rate, any type of strong clip should work. Vice-grips (locking pliers) or c-clamps would work as well.
How long you do the drip method depends on what your acclimating. If your doing this method for most freshwater species you should be ok doing it for an hour or so before introducing the fish to your tank. If you're doing this method on a saltwater invertebrate you may want to take 2 or 3 hours for this acclimation procedure. If you have a good pet shop and you trust their advice, ask for and follow their recommendations on the amount of time needed for acclimation.