Cookies are best when baked for just the right amount of time, not a minute longer or shorter. They can go so fast from golden and chewy to burned and hard; and removing them from the oven before they're done leaves them too soft. Cookies typically bake in 12 minutes or less, so take a peek at them often to prevent any kitchen catastrophes. Find the sweet spot for your recipe and your oven, and set a timer for perfect cookies every time.
Before you begin baking, study the recipe and learn what the properties of the finished cookie should be. Even if you like your cookies soft, the outer edges and surface should have a golden-brown hue. For soft cookies like oatmeal and chocolate chip, the center of the cookie should be set and not feel sticky or look gooey. Remember that cookies continue baking on a hot sheet even once they're removed from the oven, so transfer them to cooling racks as soon as possible.
For thin cookies, set the oven to the recipe's suggested temperature, keeping in mind that electric ovens and even some gas ovens can run hotter or cooler than expected. Begin checking your cookies one to two minutes before the recipe's minimum suggested baking time. Thin, crisp cookies burn easily, especially around the edges; anything dark brown means they're beginning to burn. If you see that the edges are getting dark but not done, turn down the heat by 25 degrees Fahrenheit and continue baking until the cookies are set. The end product should be firm to a light touch and lightly browned on the top.