Every Tattoo studio should have 4 separate areas: the reception/waiting room, tattooing or body piercing area, bathroom, and a separate sterilisation room.
Only a professional studio can provide the hygiene and quality condition for a professional work.
The studio and the Tattoo or Body Piercing artist should place the used needle in a yellow sharps container. All the needles should be presented to you in individual packages and opened while you are present. This is the best way to ensure that the studio does not use used needles.
The best advice is to visit the tattoo shop before getting you tattoo done. The studio need to look clean and well kept. You need to feel comfortable to ask all the question you have. The staff should be happy to introduce you to the full process and do not hesitate to request a tour.