The key to a great looking door casing, and a great looking door, is perfectly mitered corners. If you have just installed a new door that needs a casing around it or you have decided to replace the casing around an existing door, you can achieve professional results quite easily. This tutorial will help you get there by sharing a little secret - completely assemble your casing before you install it. You can also use this technique on window casings. For complete, step-by-step instructions for this DIY project, watch this friendly and straightforward video tutorial.