Stand over the fabric you're cutting. Get a firm grip on your rotary cutter - but don't white knuckle it. Give it firm pressure but don't press so hard you're making it "stall out" - roll - think roll like a rolling pin. lean ever so slightly the top towards the ruler so it doesn't go off to the side and take your time. No need to speed here. It takes time to get the hang of it, but never be in a hurry when cutting strips. Also, do check that it doesn't have two blades on - very carefully. (Try a magnifying glass - if it does use a tool to separate them - not fingers. Careful not to nick it.