I was actually going to do a writeup about this tomorrow. Tonight, I took pictures of how I feed my anemone and LPS corals.
Excellent question. I'm glad you're researching. Generally, anything of marine origin that is raw is okay for a BTA. Some people feed silversides, but I feel smaller peices of food are better. I feed mine a mix of seafood that is chopped finely. This food is great for fish as well. My clowns go nuts for it. My firefish will actually take the food out of the turkey baster.
I cut up equal amounts of squid, tuna, scallop, and clam. Then I cut up two portions of shrimp and add it to the mix. The pieces are roughly 1/8" size. Some pieces will be bigger, and some will be smaller. I rip up some nori and throw that in as well. I add enough mix to a plastic freezer bag to fill it 1/4" tall when laying on its side. Then it gets frozen. Here is how I feed it to the anemone and fish.
Break off or cut up a piece that is about an inch by an inch, or whatever size you think you'll need..
Throw it in a small plastic container and add some tank water.
Break up the mix as it thaws with your turkey baster.
Drain the water out of the container. These small particles will pollute your tank water because they won't be eaten.
Then, fill the plastic container up with water again and drain it. This should get a lot more of the small particles. You can see how much clearer the water is in this picture.
You should be left with a mix of clean seafood.
Add a bit of tank water, and suck up the mixture with your turkey baster. Squirt it into your anemone. It should grab hold of the food. A wide variety of food is good for the anemone. Here's a picture of my hammer eating. I was feeding my GBTA twice a week, because I wanted it to grow. Now, I feed it about every other week. It's still growing, just not as fast.