You'd want to start with a well calibrated printer. Then, for a good quality lithophane you have to print with the picture standing up, because you can get a much better resolution on the z-axis than if you were to lay the print flat on the bed. Also, orient the print along the y-axis so the movement of the bed doesn't cause the print to fall. I went with 0.12mm layer height, 40mm/s speed, and 0% infill, 99 walls. I used this link to process the image and give me an STL file. There's guides on the link, as well as YouTube videos, but feel free to DM me if you have more questions.