First of all, make sure that your aquarium has been established long enough to support the needs of your new addition. A good indication of your aquarium’s suitability for Tridacnids is a nice growth of coralline algae.
Make sure that your fish and invertebrates are compatible with Tridacnids. Some cleaner shrimp have proven to be destructive to clams, nibbling on their mantles and otherwise preventing full expansion. Other fishes may also harass clams. For example, I once had a Copperband Butterfly that was introduced into an established aquarium that contained clams. It never bothered the clams at all, until one day I placed a few new clams into the aquarium and he attacked them within moments. Observation and careful selection of fishes is critical if you tend to be successful with clams. I found that a good reference book to see if you tank mates are compatible is Scott Michael’s, “Reef Fish“ Do some research first.
Tridacnids do not like a lot of water movement so plan a place where you are to place your clams. You don't want a large amount of water move because we have found that in most cases that will prevent the clams from fully extending their mantles.