Always remove the selvedge. I try to keep the number of layers I cut through at 4. Any time I cut long strips I fold the fabric to not more than 4 layers, making sure the selvedges are even. Then I use the 4' T-square I bought at the hardware store for cutting drywall. The T-square is aluminum and works just like a quilting ruler - run the rotary cutter along it. The big T-square is one of the best tools I ever brought into the sewing room. I also use it to mark a cutting line on the roll of W&N; mark with a fine Sharpie and cut a straight line with scissors.