h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

the most important part of the butterfly stroke is the undulating motion of the body. The easiest way to learn it is to relax, try to move like a mermaid or dolphin, arch your back and untuck your chin to bring your head up, and tuck your chin and curve your back foward, entering the water *forehead first* to go back in. IF you do it right, you should be able to wiggle through the water without propulsion from your arms, and your stomach muscles will feel like H*ll.

once you have this straight, (your rear end should be surfacing regularly, while your head is down,)
you can move on to the dolphin kick, which is basically whacking both feet against the water simultaneously.

After that, if the kick hasnt' messed up your undulation, add the arms. move them in a keyhole shape in front of your body, then put back to your hips, bring them out of the water spread like butterfly wings, and foward, in front of your face where you begin the keyhole motion again.

There's more to all the strokes than this article makes out. According to this, you need not use your feet at all for crawl, backsroke or even breastroke. One day I've promised myself I will update it.

I taught myself butterfly in the sea. The greater buoyancy helped no end with the confidence and I could then do it in the pool without any of the ensuing nonsense regarding drowning