Ahhhh, my trusty Harry Potter scarf. One of my first projects ever made. I made two three of the most common beginner mistakes while knitting this:

1. Accidental yarn over hole! Remember those? I couldn't even remember whether my yarn went in front or back for knitting!
2. Stockinette stitch. Raise your hand if you took your first project to the yarn store to ask them how you could make it stop rolling up at the edges and they gave you that patronizing pat on the head and explained that all stockinette rolls. I ended up knitting a second identical scarf, sewing up the edges, and making a tube.
3. I used Lion Brand Wool Ease, since this was long before I discovered just how itchy wool is on my skin.