I normally start by making a plane and texturing it with the image I want to trace in Line mode. Typically the image would be a photograph of an object taken in profile from the X, Y or maybe Z direction.
The plane is initially centered at the XY origin (0,0) when you create it, but that means you can't see the Lines traced against it because they also form at X or Y = 0 (depending on what direction you're placing them) by default. So before I start tracing, I move the plane back slightly (even 0.01m is enough) so the Lines will now be visible in front of the plane.
Another tip, is to make sure (in gmax) that you select 'corner' mode before making the lines - 'bezier' or curved mode is likely to create lots of unwanted vertices in an attempt to give a smooth curved line.