Here's my suggestions in a nutshell.
Try to bring the fish up on whichever side you like to gaff. I prefer to gaff with my right hand so I try to bring the fish up on the right.
Pull the gaff into the fish, don't swing. You want to stick it, not club it. Practice with a watermelon.:lol:
I like to have two connections with the fish until secured, so I gaff, stringer, remove hook, secure stringer, remove gaff. Then bleed by ripping/cutting the gills. With a halibut, beat the living crap out of its head with whatever makes the best club. Not really necessary with a YT or WSB unless they have a bad attitude.
Preparation is great but don't over think things. Nothing beats experience and that can't be found on the computer.
As for cleaning, I fillet rockfish, bonita, and calicos on the boat but leave the skin on. Bigger fish are more trouble than its worth, so those I do as the other guys said, paddle in with it in my lap and attached to the boat by the stringer.