Teach your horse to smile
Whenever I get a new horse in, the first trick I teach to all of them is “Smile.” While it may seem like a simple, silly trick it can also be used to “load” the clicker, which basically trains the horse to understand that when I click, a reward is coming. It also can teach a horse to target your finger, which will help with other tricks and can help with trailer loading.
This trick is super fun and very straightforward. Most horses will start to pick it up immediately and completely master it in a few short sessions.