Step 1: Acquire components.
You'll need a few washers, lock-washers, and locknuts, although I'm not going to detail specifically how many and what size you need, since that depends on your bicycle. It's quite simple, just improvise it as you go. I spent about $4 at the hardware store for each of the mounts I'm about to show you, including bolts, nuts, and washers.
Oh, and for the headset-mount, you'll need an old seatpost clamp, salvaged from an old bicycle or perhaps the parts room of your local community bike shop, if you have one.