How do beginning tattoo artists practice their work?
They do practice on people. They also practice on fake skin, yes you can actually buy tattoo practice skin. Many also practice on pig skin. I know many artists who covered a dead pig in ink before they were ever allowed to go near a person. Once the pig and fake skin stuff shows that they can tattoo, they go onto working with real people, but the people getting tattooed know that this is an apprentice, not a full fledged artist yet.
just do it
They practice on cadavers.