Baking cookies could be considered as much a science as an art. The smallest alteration in the ingredients or failure to follow directions may produce a product much different from the one intended. Read the recipe carefully before beginning, and make sure you have everything you need before you start mixing the dough. Bakers with a convection oven probably don't have a problem with cookies burning on the bottom, because its fan distributes the heat more evenly. If you have a conventional oven, however, a few tips may help you keep your cookies safe from overbrowning.
Bake your cookies on a heavy, reflective, light-colored aluminum cookie sheet with no rim. Consider using an insulated sheet that has a layer of air built in, making it less vulnerable to the oven's lower heating element.
Line the pan with parchment paper to provide a bit more insulation and to encourage uniform baking.
Place a silicone liner in your pan before baking the cookies if the pan is thin. Or stack one thin cookie sheet on top of another to provide more protection from the heating element.
Bake the cookies in the top half of the oven, where the temperature is highest but the bottom of the pan is away from the lower heating element.
Set the oven timer for the low end of the estimated baking time, and check the cookies when it sounds. If your cookies are not quite brown enough, don't leave them. Stand at the oven where you can check them again as needed.
Check your oven's actual temperature if your cookies continue to burn on the bottom. An oven thermometer can tell you if the temperature reading is consistently off, and by how much.