Glenn Watt recently created a great how-to video walking you through how to create a scarf joint on a cigar box guitar neck. A scarf joint is a special angled cut which, when glued back together, angles the headstock away from the fingerboard surface of the neck at a specified angle (usually about 15 degrees). Having the headstock angled like this makes it easier to get the strings to stay tight against the nut (this is referred to as the “break angle” of the strings).
So check this video out, and give a scarf joint a try on your next build. It does take some care and attention to detail to make one, but it is well worth the effort!