I made this wall art a year ago. For some reason, I never posted the tutorial. So here it goes...
First, find some fabric you like. Get enough to cover and overlap the frame.
Pull the fabric tight, and staple each side and corner.
This is what it should look like from the front.
Arrange a pattern that is pleasing to the eye.
Then hang it on the wall. I used thumb tacks and some pins. Use whatever works best for you.