Cookies are best when they are baked the appropriate amount of time, not a minute more or less. A tray of cookies can quickly go from the optimal color and texture to burned and hard. Alternatively, removing them from the oven before they are done leaves them too soft. Set an oven timer so you avoid cooking them longer than necessary. Cookies typically bake in 12 minutes or less, so take a peek at them often to prevent any kitchen catastrophes.
For thin cookies, set your 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 are beginning to burn. If you see that the edges are getting dark but not done, turn down the heat 25 degrees and continue baking at a lower temperature until the cookies are set. The end product should be firm to a light touch and lightly browned on the top.
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 the baked goods will continue cooking on a hot sheet, so transfer them to cooling racks as soon as possible after you remove them from the oven.