Okay, good thread, but the miter is not the hardest part for me. It is gluing. You can cut a perfect 45° miter, but it won't be perfect if it is not glued squarely. I have a couple, maybe three gluing jigs. The last one I made does the best job, but it is cumbersome to set up. Okay for me because I may make 5 or 6 frames a year, but if I were to do more I would want something easier to set up. My current one is similar to this.
The other part is fastening the picture into the frame. In the past I have always used little nails, and it looks pretty "tacky" (get it?) to me. Recently I purchased a Logan Picture frame tool. It works great.