Excuse the picture quality it was taken with an old 6mp samsung compact.
Step 1: What you'll need
An old reflector: (this is kind of essential I don't know how I would have done this without it.) You must have the bracket as that will be the bit you're using. The reflector itself can be used another way (if riding fixed) as showed below
Two picture hanger things: I don't know what you call them and as you can see mine are different sizes but they can be bought from anywhere whether it be ASDA (Walmart) or B&Q.
Nuts and Bolts: Details in the picture (With the exception of '5x20mm' I don't know what any of that means.)
A spacer of sorts: In my case my handlebars were a tad narrow for the clamp which meant I needed to use one. (A bit of blue tack would do it.)
Screwdriver: Obviously the type depends on your bolts.
iPod/iPhone (or similar)
Advisory case: To avoid material damage to your device.
Ruler's just for show.