A long time ago i stayed at a friends house and when i plugged in my Iaptop the socket was loose in the wall. When i removed my Iaptop plug the back box came out of the wall.
When i came to plasterboard my walls in each room as i go along below is how i do it so as to maintain an air gap.
I put plenty of sockets using the above method to each room as i go along. Kitchen 23 sockets, Lounge 16 and the new bedroom 16 sockets. It's better to install when you are doing the work but also it's easy to fit should you find you need more. I am lucky that my electrician comes along to check i have laid the cables in correctly before he stars to connect them all up.
Each room also has it's own fuse panel or as some know it as a consumer panel this saves shutting down the whole house when electric works are needs, this way you just turn of whatever room you need the power switched of.
Screw a block of wood to the wall and then screw your socket back box to the block of wood. Simple.
This is after the back box has been screwed in position.
Hope that helps someone i am sure it will.