Anemones need a lot of light; more than most corals. If you do not have specialized lighting, it will die.
Anemones also need pristine water quality. If you have any nitrates, it will usually die.
Anemones usually only do well in mature, well-established tanks. I do not recommend that anyone get an anemone for a tank that is less than 10 months old, preferably a year.
Anemones are one of the most difficult animals to keep successfully in this hobby and so many people buy them when they have young tanks or insufficient lighting. When anemones get sick or die, they have the potential to poison and wipe out your entire tank and everything else living in it. They are NASTY when they go bad!
Of course, knowing what type of anemone you have will help greatly, as some species are easier to care for than others (i.e. bubble tips are considered the easiest, although they are still very very difficult to keep alive, wherease sebaes are usually considered near impossible to keep alive for anyone).