Just a small amount of advice for new drawers.
To draw a straight line without a ruler:
1 - Make two points,
2 - start at the farthest point from your body,
3 - look at the second point, and
4 - without looking at the pencil, pull the pencil toward the other dot that you're looking at.
It takes some practice, but at some point you won't even need a ruler anymore to draw straight lines.
Try it, you'll be surprised. This technique is used a lot in board drafting.
-Magnum