I chose an easy part of my bike to "reflectablize" as one of my friends would say. A detachable fender that I mostly never detach.
Before we begin, I must state that I tried the two main manufacturers of "reflective spraypaint" on the market. Those being Rustoleum and Krylon. The amount of reflective material in the spraypaint was almost non existent. I found that I had to do way too many coats to even get noticeable reflectivity. I ended up seeking a refund from each company. Therefore, I strongly advise you NOT to waste your money. You could always go the reflective tape route but I found it to be expensive as well and just didn't seem as cool as what I am about to instructablize you on.
Step 1: Materials list
2) Krylon Clear Acrylic Coating (or similar clearcoat paint)
3) Masking tape (if you need to mask anything)
4) Paint tray or suitably sized object to catch glass beads
5) Empty spice shaker
6) Any necessary tools for disassembly of bike part
7) Retro reflective Microspheres (glass beads)
Step 2: Prepping the part you're painting
I also disassembled the fender to make masking easier, see photo.
Step 3: Fill up the spice shaker with glass beads
You can source glass beads from several manufacturers / retailers. Google can help.
Note the gold spoon, this is a classy Instructable folks, no silver spoon here!