If possible, debarbing a hook is best done at the tying vise prior to tying a fly. With a spring-loaded vise like this one, it’s as simple as opening the jaws, inserting the hook perpendicular to the jaws and back from the jaw tip. You then slowly release the lever to close the jaws and mash the barb. Up close it looks like this: the barb should be completely mashed with only a small bump left on the hook.
A cam or lever vise will also work just fine and should achieve the same result, although a little more challenging. A vise with a thumb screw gets the job done as well. Needle nose pliers are another choice for small hooks. I prefer pliers with fine points and flat jaws as opposed to serrations. The same goes for forceps and hemostats. For smaller hooks use only the tips of the pliers. On larger hooks you need to squeeze hard to completely mash the barb. On still-larger saltwater hooks I do use heavy duty serrated pliers for a positive grip and additional mashing power.”