Here we have a video, dating from 2012, in which Pierre Bara (whatever happened to him?!) interviews Yves Beaujard.
Pierre asks Yves for tips regarding the engraving of portraits. After all, Yves, who was taught the art of classic portrait engraving in the US, is considered a specialist in this field. He not only engraved a Marianne for France, but many other portraits as well.
Basically, his main tip is to create the image first as a drawn design, working out the placement of lines, spaces, etc. The classic engraving method of crossed lines and dots is a very precise and almost mechanical process, which needs to be practised on paper first, so you can erase any 'faulty' lines.