Mitred corners are tricky to hold when gluing or nailing in place. This tip keeps your corners lined up using standard woodworking clamps and a few pieces of scrap wood.
Save the cut off wood after you cut your 45-degree mitred corners. These will be used to glue to the end of the corners with paper in between. You can then hold the corner together with a standard clamp, without the wood slipping. The video above shows the process in more detail and it's a great solution if you don't have corner clamps.
Right angle clamps or corner clamps are made specifically to hold two piece of wood together to hold a right angle. These are extremely handy when gluing mitred corners together or even butt joints. If you are in a pinch and don't have these specialty clamps available then the scrap and glue method should work.
How to clamp up mitered corners [Chad Stanton (YouTube)]