If your new LCD does not come with a window plate: Tape your old window plate in place as shown in the photo. Make sure it lines up properly and fits into the grooves. This makes re-assembly much easier.
If necessary clean the window plate and LCD with a micro fiber dry cloth. Make sure there is no debris or dust before you re-install. DO NOT use any liquids.
Now just reverse the steps to re-assemble your camera with the new screen.