, IEA stands for Interscholastic Equestrian Association.
Basically, there are IEA teams (one barn hosts one team) made up of high school student riders. Each barn hosts at least one show, and provides the horses for said show. Riders are paired with a horse they most likely have not ever met or ridden before. They go straight into a flat class without any warmup, and they get a brief one or two jump warmup before entering a jumping class.
I didn't have a fantastic experience with IEA in high school. The whole group was very cliquey and I did not fit into that clique because I was not rich and snobby and I did not own an imported warmblood like everyone else. But I think that has much more to do with the stable I was involved with than IEA itself. I mostly did poorly in IEA because I did not like riding horses behind the vertical. I got points taken off left and right for riding them on
the vertical instead of behind, despite the rest of my ride feeling and (per others) looking great. It's definitely something worth doing once and deciding if your group is enjoyable and your local judges are fair. I did the same organization except at the college level and won almost every class because the judges didn't judge off of the horse's head carriage. But please don't let my review discourage you, everyone needs to experience things for themselves before they can judge!
As for advice... Prep all of your show clothes the night before so you don't have to look for your missing breeches at 4 am the morning of. Bring extras of hair-related things (hair ties, bobby pins, hair nets) because it might just take 20 of them to shove all your hair under your helmet, and you never know when someone else on the team is going to need more. Get in most or all of your show attire at home and then put layers on top of it so you don't have to change in below freezing weather at a horse show (if you live in a cold area). Don't take off your extra layers until you are on the horse AND 30 seconds away from being called into the ring. Don't underestimate the power of hand warmers, they will save your fingers!! Always bring at least $10 in cash because lots of people will be selling drinks and food like hot cocoa and mac and cheese, and you will
want some after standing still in the freezing cold for five hours. Bring your leather cleaner/polish with you because it's very likely you'll dirty them up again before it's your turn to ride. In fact, you might want to bring a large bag with you to make it easier to tote all your stuff around, including your ribbons at the end of the day. Don't be afraid to tell a team mate your stirrups are uneven, too long, or too short, and ask them to change them for you.
And above all... Be a good team player! Encourage your peers, see if you can ride with them outside of your team time, carpool when you can, and have fun!