Cutting width of fabric strips is typically where you start with patchwork. Start with pressing and have the existing fold and selvages lined up.
Place your ruler on the fabric. (I’m right handed.) I’m cutting a 3 1/2″ strip so I’ve put the ruler at about 3 3/4″ from the edge since the left edge is not a clean edge. We’ll clean up that edge in a bit.
Be careful to align the edge of the fabric with a line on your ruler to make sure your ruler is perpendicular to the fabric edge. Do this on both the top and bottom edge checking that all edges of the favric are perpendicular to the ruler.
Cut the first strip. Move the ruler 3 1/2″ from the clean edge, align the top and and bottom edges with a line on the ruler and cut another strip. Cut more strips as needed.
Carefully turn over the first strip and align the clean edge with 3 1/2″ on the ruler and trim off the excess 1/4″. Be careful to check that the top and bottom edges are lined up with the ruler and the fabric is straight.