I show miniatures and shetland. The biggest difference is like andrea said, shetlands are more on action which is why they are asked to work the rail. I show a foundation and you will basically enter the ring at a walk and set you horse up side to side (not nose to tail, atleast i have never seen it nose to tail in ASPC). The judge(s) will then do a walk around each horse and will sygnal to you to go work the rail. Basically just trot your pony but be sure to stay a little bit ahead of the pony and kind of look back so the judge can get a good clear view. I try to keep him right at the end of the lead and as close to the rail as possible. Then turn (always turn/pivot the horse) and work the rail back, this time with the pony on the judges side and then go back around to lineup and set up.
I always slightly park my shetland and i get his neck a little different.
In shetlands the 'A' is the classic/foundation while the 'B' papered are the moderns. So shetlands do have A and B, however instead of the A and B standing for height divisions, they stand for 'type'. Does that help?