I haven't been to that gymkhana but here are some tips for the hacking and led classes.
Make sure your horse, has a nice shiny coat, plaited nicely (preferably rosettes) good weight (not too fat or thin and has some prettiness/elegance to him.
Hacking is a very precise and elegant sport, requiring the horse and rider to be absolutely spotless.
So make sure all your is sparkling like a disco ball and yourself clean and tidy.
Your workout for led will be this. Usually your horse will be shown in a bridle (or halter if Quarter Horse). Once again make sure everything is clean and spotless!
Once you enter the ring you and all your other competitiors will walk around the judge and from there she may pick 4/5 competitors to do a workout or you may all do the workout.
Usually the workout is walk/trot away from judge present horse side on and trot back again. THat is all that is required. Remember to keep him straight away and to the judge.
AND don't FORGET TO SMILE!
Also while in the line up don't let your horse rest his leg or have a bored expression on his face - try to keep him interested.
Once again clean and tidy .... :) The workout will usually be a trot figure eight and canter figure eight ( a simple change ). The only thing to remember in the hack ring is to show the judge that your horse is calm, responsive and the best.
Good Luck !
Let Me Know How It Goes!