[header] How to make rainbow cookies [title] Preheat the oven and arrange the oven racks. [step] To be certain the the oven is warm enough when you bake the cookie layers, it's important to preheat the oven. Set the temperature to 350 degrees fahrenheit (180 degrees celsius) and allow it to heat. 
Position the oven racks in the upper and lower thirds of the oven as well. [substeps] Be aware of how your oven indicates that it's preheated to the desired temperature.