Hi,
there is no best advice unfortunately. The best way i found for me is to project or to drape a line of the proposed road on the terrain. Then i select the line piece by piece and weld it. Then i use the FollowMeAndKeep tool to generate the profil of the road along the line. Then i remove all the overlapping faces of the terrain and use the sandbox tool "From Contours" to modify the terrain step by step.
The result almost looks like a real street, but not quite.
Karlheinz
Terrain.jpg
Terrain.skp