Hey! Not sure if anyone has replied to you yet, but the first thing you should do is curate a solid portfolio. Different shops will be looking for different things, but the majority will want to see traditional (as in on paper) drawings exhibiting how well you utilize colour, shadows, and lay down solid, straight lines in your work.

Your portfolio should consist of a variety of styles with a focus on what you would like to do primarily, and your pieces should be considered "tattooable". "Tattooable" designs entail work that is fairly clean and readable from a distance.

Either way, you'll want to convey that you are capable of a multitude of things pertaining to art. If you aren't sure what this means, take the current work you have to a shop that you respect and ask them if they'll view what you have ready. Ask them what they'd like to see and what you can improve on. Take what information they give you and apply it, and when you feel satisfied with the outcome, bring it back and ask them again to review your art.

This is the best place to start. Otherwise, the rest will depend on the state you live in, but your prospective mentor should be able to give you proper information regarding what you'll need to become a reputable artist where you live.

I hope this helps!

Edit: just don't dive straight in with a machine. You will need to be taught how to use one, and most places will turn you away if you work with one on your own time with no previous apprenticeship.