As you can see, I opted for irregularity as I trimmed this piece. To achieve this look, while also having a piece that would hang straight, I first trimmed it to a perfect, straight edged rectangle, then took the scissors to it to create some waves to the edges.
One of the nice things about having a solid, contrasting background is the way the stitching shows up. However, having all that stitching show up so clearly makes it possible to see every single irregularity and tension problem, etc. This piece is intended for an invitational show - don't expect to send it to a judged show, so I indulged myself and went with the solid black backing.