Your vet should have showed you how to administer the first dose. At our clinic, we show how to give the first injection, and if they are AT ALL nervous or unsure, they can come in and we will administer the injections at no charge. If you didn't get it from a vet, you shouldn't be using it.

Upper third of the body, feel for the spine and inject into the the muscle along either side. Try to get in between scales if you can. Baytril is tricky, because you want to get it deep enough that you don't cause skin reactions (which is the main cause of scarring from Baytril), but you don't want it too deep either. It's best if you have two people, one to hold the head and one to poke.