I pin perpendicular. I think I was taught that way, all those many years ago. I will also tell you that when pinning fabric to applique, I often use 2 pins, or make the pin go through 3 times. I was instructed 1 pin is a pivot--it moves, that's why I often use 2 pins or make an in and out and in again pin if there isn't enough room for 2. Boy are we persnickety! (That was one of my Grandpa's favorite words.)