
Once  you have looked and seen what is actually out there, you can  proceed  with your tattoo designs from your initial idea or concept,  whether you  have written it down or drawn a small thumabnail sketch as a  reference.  I usually work this way and it provides a really useful point  of  concept design in stages and you could later see how your artwork  has  developed from the draft stage.
So to draw a demonic tattoo,  you just  start with the shape of your demon, drawing loosely you pencil  in the  structure of the demon, however you want it to look, you could at  this  stage just draw the head of the demon or the full image of the  demon if  you wish, it's really up to you!