I catch fish easily by using a 2 liter bottle. Poke a few small holes in the bottle to reduce the drag when you pull the trap out. Cut the top off and toss it. Take a peice of eggcrate a little bigger than the size of the hole left when you cut the top off. Use a bit of fishing line to secure one edge of the eggcrate to the the bottle (poke a little hole in the bottle) so that when you lay the bottle on it's side, the eggcrate lays flat, like a little door matt. This is the hinge for the "lid" that closes the fish in when you trap it. Then, on the side of the eggcrate piece opposite from you hinge, tie a piece of fishing line, then run the line through the top of the cut part of the bottle, so that when you pull the line, the eggcrate door slams shut. Run the line out to a convenient tank watching chair.
Leave bottle in tank for fish to get used to, you may need to put some small rocks in the weigh it down. Feed fish frequently in the bottle so they get used to going in there.
When you have seen the fish go you want to catch go in the bottle without fear, grab your beverage of choice, put food in the trap, and just wait. ( it took about three short sittings of this for me to catch my flame angels, but it was worth it) You want the fish you are trapping to be well into the bottle, I don't always trigger the trap as soon as they go in, I wait until they are well in the bottle, because if you try to trap them too soon I imagine they get scared it will take forever for them to go in again. But I have never had one escape the trap on me when I pulled it.
So when your fish is well in the bottle, PULL PULL PULL on the line, the lid snaps shut and the trap zips up to the surface.
This is really easy, I had to catch two flame angels out of my 155g reef that was full of rock, and it was no problem, just took a little patience. They are very smart fish and would not be fooled by the kind of trap with an inverted 2 liter lid, I know they would be able to find the escape when I was pulling the trap. I also catch my foxface this way to move him from tank to ank to eat excess caulerpa.