First thing to do when you get your new clam is to check water temperature and salinity in the shipping water. Write this down, you want to slowly change this to the same as your tank waters parameters.
Next unpack your clam and place it along with some of the water your clam came in to a separate container. Do this under lighting that is not intense, your clam has been in the dark for a while. It needs time to adjust.
After you place your new clam in a separate container with some of the shipping water start to add water from your system. I would do this in small amounts half a cup or so.
Continue to do this every 10 minutes until you have doubled the water volume that you started with. Then empty about 50% of your water down the drain.
Repeat the above procedure again until salinity and temperature is the same as your tank.
Before putting your new baby into the tank, turn off your lights. Your clam needs to be slowly adjusted to the new lights. After a couple hours in your reef, you may start to acclimate your new clam to your lighting. If you have separate controls for different lights, try and use the lights to the left or right of your new clam. I would be very carefull with your lights for a period of about a week. Start your clam lower in the tank and move it up as it gets used to your lighting. Some clams will attach quickly to their new home so be carefull in your placement. Once a clam has attached we do not recommend moving them, so placement is important. When moving your clam up your rockwork to it's final position it helps to place it in a pvc ring about the same size as the clam. This will ensure that your clam does not attch until you want him to. Make sure your pvc ring and clam are stable so it does not take a nasty spill. Pvc ring only needs to be about 1 or 2 inches thick.
Some people like to do a drip acclimation which also works great. If you use drip meathod make sure you warm up the clam by floating it first.
Best of luck, Rob