I send about 20 frames out to all parts of the world, never had any damaged in transit. touch wood...

I flatten a bike box, then cut it in half to make two frame sized boxes.
I take the forks out the frame so the pack is smaller, saves almost 1kg ($$)

Try and make the box a tight fit so the frame does not rattle around, I wrap up the rear-end in bubblewrap+cardboard and the headtube and bb.

Use lots of brown tape, when finished you should be confident enough to throw the box around and drop it off a table, even stand on it. (thats whats going to happen to it anyway)