You will need someone who can guide you in the process of backing up and parking the truck with a horse trailer. The person can guide you with hand signals as well as talk to you during the process. Horse trailers are pretty large and can be hard to move back on your own. The person can also let you know when to stop if you are getting too close to the curb.
Keep it Aligned
Try to get in line with the parking spot early as you move back. If the space that you have available to backup is limited, this will be difficult. The idea is to get in line with the parking spot early so that you can back up straight and have no issues when you are parking.
Keep Your Eyes Back
Make sure that you are looking back when you are backing up the vehicle with the horse trailer. Try to make maximum use of both sides rear view mirrors. Your front rear view mirror will not be much use as the trailer will be blocking it. Also, it is not a bad idea if you turn your head back to get a clear view. Objects in the mirror appear closer than they actually are and in some cases, rear view mirrors can be slightly misleading.
Take it Easy
There are generally no points for parking in a hurry though you can hit the trailer with the curb and beyond. Take your time and make sure that you are not rushing it. This may save you from a lot of trouble. Make sure that your speed is slow and you can easily break once you reach the desired point.