Hole, then

The dowels are installed in the hole, then the brackets are attached, the guide rails are attached to them, while the vertical of their installation and their parallelism in one vertical plane are checked. On the frame, before fastening with it with drywall, you can lay all the wires to the switch and sockets. The seams between the sheets are putty, sealed with a painting grid (the heads of the fixing screws should be drowned in the surface of the sheets), putty is applied with a thin layer to their surface, which is grinded after the putty dries. The wall is ready for painting or pasting with wallpaper.