GaiGai gave excellent illustrations. Many quilters match up the selvedges and then cut. The selvedge is not important, but the fold is. If you cut straight from the fold, it does not matter that the selvedge does not line up.
Starch is your friend.
Sandpaper on the back of your ruler is helpful. Use an office supply cheapo punch, fine sandpaper & glue on with rubber cement. If all else fails, just use the rubber cement!