I know a lot of people already do this, but I'm always surprised by how many people have no idea that you can do this, so here goes.
Using parchment paper to bake the cookies is easy, safe (and food-grade!), and is my favorite cookie-baking trick.
Parchment paper allows you to be more precise in baking cookies, because you can remove them all from the pan at the same moment. Plus, you can make more cookies faster, which is never a bad thing.
A note: Some people use brown paper, but parchment has a longer life, so I prefer it over paper.
Step 1: What to Do
All you need to do is cut some parchment paper that will fit on the cookie sheet you're using. Put the dough on the parchment like you normally would. The difference here comes when you pull it out of the oven. Wait until the cookies are exactly the texture/color/whatever that you want. Pull the pan out of the oven, and slip the parchment paper with the cookies on it onto a dry surface.
Step 2: How Is This Different From the Way I Normally Bake Cookies?
Well, with this method the cookies stop baking the very second you slide the parchment off the pan. Without parchment paper they keep baking, even if it's just a little, until they're off of the pan. Typically you have to wait until the cookies are crispy enough so you don't destroy them when you take them off the pan. This way you can take them out of the oven even when they're still moist and chewy on the bottom. Granted, not everyone likes soft cookies, but that's just one advantage to baking with parchment.
For people like me, being able to remove all the cookies at once saves me a lot of frustration, probably because of simply knowing that all the cookies will be the same (There's some of my geek-ish OCD tendencies showing through again, oh my.).
Not to mention, sliding them all off at once saves a lot of time, which is definitely good when you're trying to make hundreds of cookies at a time.
Step 3: What Now?
Roll up that parchment and enjoy your perfect cookies! The great part about using parchment is that the paper is re-usable. Stick it away and use it again next time. I re-use it until it literally falls apart.