There are few ways to learn tattooing and the best one would be good apprenticeship. In this modern age of internet and information people will learn themselves and there are several negative things on that like you would never know what you don’t know and what you have understood not really as it meant to be while when you have someone looking over on what you are doing you get tips straight away.
Important part of learning tattooing is practice and again – chance of messing up is huge if you do it on your own. Big help is practicing on practice skin or whatever your medium is apart from something living. In apprenticeship or at least having someone experienced around is best learning way possible where your teacher can point out your errors and show best ways of doing it.
Never stop learning and practice makes it perfect ( hopefully )