Make sure to leave room between cookies on the cookie cookie sheet. Usually a good rule of thumb is 2 inches between cookies. If they are extremely large cookies or the recipe calls for more space, adjust the space.
Use a baking sheet that is at least 2 inches smaller all-round than your oven. This will allow for the proper circulation of hot air. For that same reason, usually bake only one sheet of cookies at a time. If you use a convection oven, this is not an issue.
Cool cookies on wire racks. This will allow the steam to evaporate and will keep your cookies from becoming soggy. This instruction is very important and you will find it in all cookie recipes.
Use a pancake turner to remove and move cookies from baking sheets. This will keep warm cookies from tearing or breaking.
Watch the baking time. Always check cookies at the minimum baking time. Even one minute can mean the difference between a cookie that is done and one that is ruined. Immediately remove from the baking sheet with a pancake turner unless the recipe calls for them to cool for a specified time on the cookie sheet.
Use an accurate timer. Try using the timer on your microwave or try the great little timer from Pampered Chef. They are both VERY accurate. Most of the department store kind are ok but not as accurate.