I have had success in the past of just putting a net in the tank on a frequent basis, with no intention of doing anything with it...I also will feed from it, fish will go into it and eat. That way when I need to catch a fish they trust it...I put food in, and they go into it and bam, I got my fish...also being slow to move it helps...fast moving things scares fish by nature (its a live saving defense mechanism and that cause them to dart into hiding...and most people try to go afte the fish fast, and they just hide instead of "sneaking" up on them.
Its a myth that fish do not have any sort of long term memory...they do and they get used to certain things, after some time...