Need tips on hard surface curves im working on pot of greed from Yu Gi Oh. I have modeled the base mesh and was wondering if anyone has any tips on doing these curved  lines highlighted in the image below.

Thanks in advance!
You can add a Bezier curve, project its vertices on the surface using the face snapping option (as you grab a vertex, it will be projected onto the nearest face, according to the view), then create another curve to set the profile of the line (choose it as Bevel object).