I won’t speak for all but the sights on my .470 double rifle were coarse express sights. Shallow V with a fair sized bead up front. With that in mind I figured if I could keep all my shots in a 6 inch circle at 50 yards I’d be doing good.
Rehearse the shot sequence as though the PH has just set up the sticks. Make that first shot your best effort followed up by a very quick second shot. By any means possible, stay on the sticks for your immediate second shot. No sense in offhand shooting if there’s a perfectly good rest right in front of you. My practice has always been to continue to shoot until I see the results I want on game, (hooves in the air).
Learn to run your gun quickly and efficiently on reloads, brass be damned.
Another thing I did, YMMV, once I figured out that I could hit what I was aiming at, I shot my .470 very little. Maybe 4 shots per range session max, then take a break for a few days. If you’re the rare bird who shoots a .470 like it’s a .22 long rifle, ignore that last bit.