In a previous post I've talked about score pads that are for helping create perfect creases in your card stock. A score pad though, can run you $20-$30 depending on the brand, what little features it may have to offer and so forth. I figured out a free way of scoring paper.
What you'll need:
Your card stock of choice
A butter knife
A pencil (optional)
Take your card stock and figure out where you want your fold. If you want, you can use a pencil to mark your fold line, but it isn't always necessary. Then, take your ruler and place it where you intend to fold your paper. Take your butter knife and move the edge (NOT the serrated edge) along the side of your ruler like you would a pencil. You may need to do this a couple of times for heavier card stock. This will create an indent in your paper. And now, fold. You'll have a perfect fold without those little wrinkles.