Anemones aren't that hard to keep but do need clean water, good light and a bit of food.
Depending on how tall/ high the tank is will determine whether or not you need metal halide lights. In a shallow tank up to 18inches high, you can use a couple of fluorescent lights. T5s are better than standard T8 globes and if you get high output (HO) T5s then they are better again. In taller tanks, say 2ft or more then you want halides.
If your anemone is getting enough light it will go brown or green. If they don't get enough light they go white and usually die shortly after.
They require good water quality with minimal nutrients. They like a bit of water movement but not too much and definitely no powerheads blowing directly onto them If they don't like their position they will move and usually crawl off under a rock. Here they sit and don't get any light and gradually fade away and die.
If your anemone does crawl under a rock try to move things around so it can get some light. Don't try to pull the anemone off a rock tho because you will tear the basal disc (its foot) and that can kill it. If worse comes to worse and you can't get light to it then move the rock it is on. Eventually they settle down somewhere and when they find a good spot leave them alone.
They don't need feeding if they have sufficient light but do better if given a bit of meat food several times a week. They will eat all sorts of things including whole whitebait, but this should not be done. If an anemone is given too much food they will eat it all. But an hour or so later they will puke it back up and it will cause water quality problems. They should be fed a few small bits of fish or prawn. The particles of food should be about the same size as an adult brine shrimp. Drop 3-4 pieces into the tentacles every now and then and leave it at that.
You can feed them every day if you like and they do well with the extra food, but you have to keep a close eye on water quality. The more food you feed them, the faster the tank conditions will deteriorate.
Bubbletip anemones (Entacmaea quadricolor) are the easiest to keep.