I think working slowly and staying calm is the biggest thing with sorting. And learning how to read the cattle. Horses usually figure out how to read cattle, too.
I guess if your horse is scared, you'll just have to stick with it. Maybe let him hold the line (or gate, or however they do it), at first if he's scared. Show up early to warm him up really well and take the edge off him so he's not as nervous.
Does your horse like to chase stuff, such as dogs? If so, that's a sign that he might like herding cattle.