Covering the corners of boards is a frequent bookcraft task. The various ways of covering a very thick board are demonstrated here. The thick board is used to show the details of the technique ~ they do not show up clearly on normal weight boards. I leave it to you to decide which method is best. Anyone with just a little careful observation will have noticed the way in which 'everyone' does it. There must be reasons for that!
The techniques shown here are those that apply when using thin boards ~ up to a few mm thick. Making corners when covering boxes is completely different [102108].