to avoid it fraying i tend to get the fly line just inside the braid so that it frays with the fly line in my right hand i use my nails on my thumb and index to hold those frayed ends onto the fly line then with my left push the braid so it opens up and then release so that it jumps into the fly line
feed it up and then gently slide the plastic sleeve over the fly line which and stages ive used my teeth to slide to stop the braid from moving.
once its on it still can come off, been a few times when ive been fighting fish and slip its gone.
so i add a spot of glue on the ends of the plastic sleeve, ive also tried using a blood knot right on the end of the flyline over the braid to try hold it aswell but my knot tying skills are still not the best and it slipped