There's something to be said about having a happy horse. It makes everyone associated with the horse-the barn manager, stablehands, riders, instructors, and even the other horses-lives better.
First, how can you tell your horse is happy? Since horses can't talk, you have to read their body language. Are they interested in things going on around them? Do their ears flicker back and forth? Do they have bright eyes and a shiny coat? When you ride, does your horse seem excited to be ridden and interested in the work you're doing? Then you have a happy horse.
But what if your horse isn't happy? How can you make a happy horse? First, your horse must be healthy. Adjusting your horse's feed can make a huge difference. If your horse isn't getting the proper nutrition, he can't be happy. Even if your horse is getting too much of a good thing, like too much protein from a high-energy alfalfa, he can be unhealthy and unhappy. Make sure your horse's feed and workload go together to get your horse in great condition.
Second, you need to make sure your horse is doing work he loves, or even likes. I once had a gelding that was a superb mover that I bought as a dressage prospect. Once I started working with him in the ring, however, I soon realized that he hated it! He would pretend-spook at things like chairs because he was so bored going around the ring! When I would take him on trail rides, he behaved himself 10 times better and always had his ears forward, interested in everything. I ended up selling him to a western rider who did trail-only. He loves his job now, and that was worth more to me than forcing him to do something he hated because I wanted him to.
Now I'm not saying your horse has to LOVE everything you do with him. Some horses just want to stay in the pasture and eat all day! But as long as they don't HATE the work you do, you will have a happy horse.
So next time you're at the barn, find something that makes your horse happy (if you don't already know) and do it!