Looking for an apprenticeship?
It's quite likely we are not a great fit. But these are some commonly available foundational materials that I trust...
Fireside Foundations - Jake Meeks
A great foundational course that will really challenge you to simplify your thought process down to a Shapes-> Values->Contrast->Edges->Color that really helps to visualize projects in a manageable way. Jake has been sharing with the tattoo community for years and has really broken things into manageable bits and runs a great group to dive into the topics if you are looking for community.
Reinventing The Tattoo - Guy Aitchison
If you don't know. Guy Aitchison is one of the greats with a passion for biomech. He has had Reinventing The Tattoo to help educate artists for decades and now there are even online groups dedicated to drawing for tattoos each week. You should at least be familiar with their offerings.
Artists complete guide to drawing the head -- William Maughan
This book was instrumental to my understanding of realistic tonal drawing and the topics of Sfumato and Chiaroscuro. It is definitely worth spending a few bucks on.
TattooNow - Gabe Ripley
Learn your booking system early. Gabe has a great group for DIY artists who need help wrangling their booking.
Dynamic Bible - Peter Han
This book was instrumental to my understanding of realistic tonal drawing and the topics of Sfumato and Chiaroscuro. It is definitely worth spending a few bucks on.
How To Draw - Scott Robertson
This is a bible on drawing, there is a companion book that is called "How to Render"