UPDATE 1/21/17: I have a new version, Mitered Granny Square 2.1 which is a diagram for a mitered square with ch2 corners and ch1 in between the 3dc clusters that you may want to check out.
To help understand how to do the Mitered Granny Square, here is a diagram. The diagram only shows the first part of mitering to get you started, it should be easy to extend it to additional rows as needed. The border is included.
These are pictures of a couple of things I am working on right now.
Some granny squares in my latest favorite colors…
These are being joined together to make a table topper for the very table I took the pictures on. I don’t know what I am going to do for the border yet, maybe a shell/scallop edge.
And my other big project, a mitered crochet blanket. I have quite a way still to go on this, but I really like how it is coming out. A bit blurry photo, but it gives you a straight on view. I plan on writing the pattern for this granny square in the not too distant future.