Roughrider has it. A single video can't come remotely close to the details this book goes into explaining EVERYTHING about training a blood tracking a dog. A incredible well written book that's worth it's weight in gold if your considering training a dog for this purpose. Highly recommend this book and as a pun I have no dog in this fight! lol But it helped me make a family dog into a working dog that absolutely loves to help find my deer.
However I have to say that not every dog makes a excellent tracker. Some just have it,some don't and some just try like hell but don't cut the mustard when the chips fall wrong. There's a huge difference of a dog that wants to and dog that will die trying! Often times the biggest hold up in the process is the dogs trainer! But if your a dog person you will bond with your dog, learn more about your dog and yourself than you ever thought possible, if you take this step! I highly recommend it to anyone. It's illegal where I live so I just take my dog for walks this time of year with no weapons other than my legal CC permit.