Horses are great at learning habits really quickly.
Now this can be a bad thing and a good thing! Whilst riding it is important to be aware of the habits that you may be creating and always try to establish good habits with your horse.
An example of a bad habit would be allowing your horse to canter back towards the property when out on a trail ride. Eventually your horse will learn this is the new normal thing to do. If one day you don't wish to canter back your horse may become quite upset with you and throw a bit of a tantrum, or your horse may be a bit excited and take off at a gallop back to your property and you won't have much control.
An example of a good habit that you can establish is if your horse comes back from canter in to a really fast trot then you can establish doing a small circle as soon as you come back to a trot. Eventually your horse will start to prepare for the small circle and slow themselves down in preparation for the small circle, resulting in your horse coming back to a nice steady trot.
So make sure you are aware of any type of repetitive behaviours that you are doing every time you are with your horse.