All good advice here-I can only ad to be sure to "measure twice-cut once"! In fact, before I swipe my rotary cutter, I always take a second (or third or fourth!) look at the measurement -also scan up and down the ruler to make sure it is straight-then slice. Also, be sure to even up one end of your fabric where you will begin cutting. Cut it straight using the FOLD as the straight guide, not the selvedges. Hold the ruler firmly and steady and make sure your fingers are out of the way of the cutter!! Good luck!