At 18, my mum knew I wanted tattoos. She herself had five small tattoos, from dedications to her Dad, to a black cat on her hip and a rose on her ankle, plus a little tribal here and there - it was the 2000's and tribal was very fashionable.
The best advice my mum ever gave me - which was also a rule - was to wait. Wait til I was 18. Of course, we all know this is the law too, but it would be naive to say that everyone abides by it. But I did.
My mum's other advice was to go somewhere really good with a good reputation. I ended up going to the same place she went for hers, on my birthday, and the entire studio sang Happy Birthday to me.