Don't buy one if your tank is less than 1 year old.
Don't buy one f your water parameters are not stable.
Don't buy one if you don't have very intense lighting on your tank. This is essential, without enough light they will slowly starve to death.
If you have a well established tank with enough light for an anemone there isn't much to their care. If you don't it will die.
I'd recomend a bubble tip, relatively easy and many clowns will go to them.
Do buy a healthy one to start with. It should have good color and be sticky to the touch. Pale or white anemones are not healthy. If the tenticals are stubby and the mouth is hanging open the nem is not healthy.
Do cover power heads with foam. Anemones wander.
Do feed every week or so.
Don't try to move it once it is in your tank it will find the place it likes?