I use a Safety Planer in my drill press to plane gradual steps in the top. First I draw lines to mark each step. The position of the lines is eyeballed according to how I want to shape the curves. Since the highest part of the curve in at the center of the body, it'll be left the full thickness of the top. Each step drops slightly with the last one at or near the edge depending on how I want the curve shaped. The guitar pictured here will have a shape similar to a Les Paul, so the edge will be about an inch and a half wide all the way around except at the waist where it'll be narrower. Each step is about 1/16" lower than the previous one. If I have a top that is 1/2" thick, and I have 6 steps down from the center section, the top will end up with a thickness of about 3/16" at the edge.
Since I have to work from the center out, I have to plane from the edge all the way in toward the edge of each step. This destroys my lines, so I have to redraw them before I plane the next step. For that reason, it's a good idea to draw out the lines on a separate sheet of paper and transfer them to the body for each pass of the planer.
The edges of the steps won't look as nice as if they'd been cut with a CNC router, but it doesn't matter since the steps will be blended together.
Once the planing is finished, I'll start blending the steps together.
I've tried belt sanders, drum sanders and random orbital sanders, but the best way to blend the steps together is to use some simple hand tools.
After the steps have been blended, I'll go over the top with some 80 grit sandpaper and fine-tune the surface.
I still have some detail shaping to do, but you get the idea. And that's how I carve an electric guitar top.