I seem to bring up pencils a lot (not alot) on my blog. I took a drafting class a few years ago and I learned that when you draw a straight line with a pencil, you are supposed to rotate the pencil in your hand. This is crazy hard. Try it.
It keeps the tip of the pencil nice and pointy, and some drafters argue that you lines are more straight and even. It is definitely is a skill you need to practice. Practice it all the time. And when people ask you why you're doing it, you can tell them that old-time architects, drafters, and you are the only ones left on the planet that do this.