Before fitting a garage door make sure that you have a drill and driver bit kit with fixings as well as a stepladder ready to fix the door. This prevents having to move around unnecessarily while working.
Make sure to have two people to lift the door. When lifting the door, have one person on either side of the door so that it can be lifted up more easily. Ideally, there would then be a third person who could fix the door to the runners and wall, but this not required.
When fitting an electric door, make sure to turn the mains power off before wiring the control box and panel.
Make sure the door is evenly positioned before completely fixing it. If it happens to be loose, remove the loose screw fixings and insert a brown raw plug. Then re-screw and finish fixing the door.