As always you sketch first on the bg layer, using the rectangle tool or white to lighten the bg. If you don;t undertand check out sketching
Final lines on this layer
Use this to erase
After Sketching begin the lineart on the Fg layer. Solids are pretty easy to use when it comes to layers, so if you screw up it won’t be too much of a problem to fix.
Can color on this layer
Use this to erase
unlike watercolors lines where you MUST color on the BG layer. you can use the fill tool and color on the FG layer. This way it’s much easier to do the background ( IF you do it on the BG layer of course. Always use white to erase though!