The best way I learned was from Becky Goldsmith. She said to start with one end of your binding already cut at a 45 degree angle. When you reach about 12" from that first end, you tuck your longer end into the beginning end; draw a line on the longer piece where the 45 degree piece ends. You just put your ruler on the 45 degree mark and cut 1/2" past your mark. Now you have two 45 degree angles and you sew a 1/4" seam. Works like a charm; perfect binding every time without all of the extra measuring.