Why are you afraid of your boss? That is probably the best place to start. Take a deep breath and a step outside your comfort zone, and ask for a lesson. Start with one, and see how you feel. You are a perfect student for dressage (or any discipline) because you have a horse of your own. Your boss will likely give you a few things you can work on with your horse alone.
Generally speaking, I start on the longe line when I have a student who is new to dressage and has their own horse. Learn to longe properly, and learn to look for true balance from the ground first. You should be able to see when your horse is carrying himself with control and balance, and when he is running in circles not using his brain or body at all. Once you can identify the type of carriage that is balanced from the ground, you can then try it from the saddle. It should feel different, much like it looks different from the ground. Start with walk/trot only and be patient. You will only honestly get what you are looking for if you are patient enough to encourage it and put in as much time as it takes. Reward him for any attempt, reward him for one balanced stride, reward him when you can tell he's trying.
"The barn taught me passion... Not the passion of winning-but rather the passion that you feel when you have nothing left but your love of something. The passion that is there when exhaustion steals your strength and frustration takes your hope."