Im going to talk AERC events as opposed to CTR, First off check the websight, register your horse and join. Check the calendar and look for events with you that offer a Limited distance or LD, ride, usually 25 miles.
Lets say ride is saturday,,,,, plan on arriving early friday, check in find out where the vet check area is and where to park your rig,
Set up your camp, get horse settled fed and watered. Don't switch feed, give him his normal stuff normal time, CHill for awhile till it is vet check time, then grab your horse walk down and let vet check out horse and fill out your form. Make sure your horse will trot/gait/ or run behind you on a lead line, you need to do the trot out 250 feet and back. Vet just basically looking for a baseline this time.,
Riders meeting friday,,, they will put out your start time, start place and vet check place, oh you want an all vet checks at camp ride, as oppossed to one way ride.
So at sat am usually bout 7, you gather round start point. I recommend you be dismounted, let the start signal go and the sprinters run off, walk down trail a bit get youtr horse focused then ge ton and start going, get the pace and keep it up, based on you're prior training, look for water breaks, maybe even a 5 minute grass break along trail,, about the 12 mile mark you will ccome into the vet check, drop your tack get in ,line to find the pulse down dudes. They have a gadget they put next to your horse to measure pulse, once pulse is 60, your time stops, you go to vet repeats exam, if all is good you get a break, depending on ride bout 30 or 40 minutes. Go back to your area, chill eat let horse eat drink tack up head back to start line, and do it again.. this time you will come in and be done with your first LD.