I am SO the worst person to answer this as I am so new.
I found it goofy at first to hold my whip 'up' as I kept wanting to have it running down,cross and away from me like I do with a dressage whip when riding. After the first half dozen ground drives though, it felt better.
I carry it at maybe 45 degrees? I don't tend to need it much. I use it to compliment my voice/rein commands if my horse needs more prompting. So say I am asking for a turn to the left and he is not responding as well as he needs to, I use the lash of the whip to give him a little tickle on the off-side, which he knows to move away from.
When halter training him (he was completely unhandled when I got him in Jan,- we had to 'run' him up into the trailer
) I did it all while using the voice commands I would be using later for driving. I find he responds really well now that we are ground driving, so the whip is really not necessary. Also at that early handling point I also carried the whip and used as an extension of my arm to move him around for grooming to get him used to moving away from it.
I have only ever given him one decent 'whack' as he threw a tantrum in one of our early sessions as he wanted to stay and attempt to eat grass and I did not share that goal of his
He did some pretty impressive plunging about/jumping up and down on the spot/rearing/bucking, so I gave him a singular quick whack with the whip and he moved promptly on out of his 'tantie', never had him do anything like that since, so I think my response and use of the whip must have been judicious.
So that is a rather newbie perspective, hopefully someone else comes along as I might be so wrong