Tone your arms
Both on and off the saddle, being around horses can help improve the strength and appearance of your arms.
You will notice when riding you often use your arms to guide the horse around the arena, and each time you alter your body position you will end up working every muscle in your body, including your arms.
What you may not notice is that you still work out your arms even without being on a horse. Every time you lift a saddle onto your horse you are working those triceps and if you start working with horses, you may start mucking them out, changing hay nets and filling up buckets - all of which involve a lot of arm work. In fact, working for one hour on the yard doing chores like this can burn 280 calories, which is the same as 40 minutes of jogging!
A way to improve your core strength and upper body balance is to do lateral raises. An easy way to do this would be to try out a rein free lunge lesson and this will also help to increase your stability in the saddle whilst giving your arms a good workout.