When making my River tam jumper I found that because I had left my crochet hook at my parents and I didn't want to bother buying a new one so I made my own. I was relatively easy to use but I should have sanded it more as the wool I was using was quite fuzzy and therefore would catch on any bumps.
Based loosely on this tutorial:
BTW: be careful using a penknife. If you can think of a better, safer way to whittle this then use it!
Get a wooden chopstick and cut off any tapered ends so that it is of uniform width. Cut to a suitable length (you can use a sturdy pair of scissors).
Whittle the length of the chopstick to just a bit bigger than the width you need.
Make a notch near one end of the chopstick and whittle it out into a crochet hook shape.
Make the end nearest the notch into a blunt point.
Use the nail file to smooth the wood and use your new crochet hook.