Work on relaxing the horse and basic figures, search some dressage tests and train your horse in the activities asked in that with some help from the internet. But, an actual instructor on the ground is still the best.
You could try YouTube for some basics but the best option would be to try to find a second trainer who specifies in dressage
Try to find a barn that has good dressage coaches
I can teach you. If your in northern California.