It’s crucial to teach your horse to stand still when you first mount, according to trainer/clinician Julie Goodnight. The lesson will help your horse know you’re always in charge. Trainer/Clinician Julie Goodnight.

When you’re ready to mount your horse on the trail, insist that he stand still until you’ve given him a specific “go-forward” cue. He should never walk off just because another horse in your riding group has moved ahead. Allowing even one unauthorized step likely will cause him to make other unauthorized decisions. 

To teach your horse to listen to your cues, mount up, and say “whoa.” Keep him still for up to a minute before trotting down the trail. Be conscious of any attempts to move. If he does so, gently pull back on the reins and say “whoa” again. 

Make standing still a habit at the start of every ride and every time you remount. Once your horse understands that you're in charge, he'll also pay closes attention to your other cues.