A really good book is Heiki Bean and Sarah Blanchard's "Carriage Driving: A Logical Approach through Dressage Training." It's for big horses but the training is exactly the same and it covers everything from handling through picking equipment, proper fitting, how to harness, ground-driving, long-lining, first hitching, etc., all the way through upper level competition driving and handling/hitching multiples. It's a wonderful resource! I haven't watched any videos yet as I considered them too pricy.
Leia