Before you go to shows, i think you should find an arena to practice in. Try keeping him against the wall at all gaites youd like to perform at a show. Once hes okay with that, bring other horses into the arena with you. See if hes okay and focused ONLY ON YOU! if hes focused on other horses, he will not do his best at a show. Teach him how to listen to you by correcting him when he looks at other things or doesnt have his ears pointed at you or forward. He should eventuLly get used to other horses. Also, trail riding with one other horse or alone could help !