quite simply go to the artist you are going to use, they will do a drawing for you, its part of the service….. they may charge a small fee for their time but they will take that from the cost of your tattoo, kind of like a small down payment, so you dont waste their time.
try google.com and search for images, or deviantart.com
you didnt even say what kind of things you like or dislike, so nobody could offer to help
ps… welcome to the forum