If you've got your hands on a pattern that you think you'll use in more than one size, or you'd just like to keep intact...here's a trick that'll have you whistling while you work:
Buy Freezer Paper from the grocery store. Trace your pattern pieces onto it in the size you'd like to make.
Cut pieces out and iron them onto your fabric for just a few seconds until they stick
Cut the fabric around the pattern using a rotary cutter or scissors,
then peel it off to use again 3 to 4 times.