If you have plants around where you keep your chickens and it isn't too humid outside for moisture to evaporate, spray/mist the plants. As the moisture evaporates off the plants, it cools the air around them.
Make sure they have a place to dirt bathe so they can dig down to where the earth is cooler and lay in it. Again, if it isn't too humid for moisture to evaporate, spray down the dirt to cool it. Just standing/laying on cool dirt helps with heat exchange. Shaded concrete/stone/brick/etc also stays much cooler so if they have access to it, let them stand/lay there.
White reflects heat so painting things white can help.
Spray the roof and outside walls of your coop as necessary througout the day to cool it.
Make sure there's efficient airflow.
Cold treats like frozen fruits and veggies work just like ice cream or a popsicle for people; the proximity of the mouth to the brain means that eating cold treats helps cool the blood flowing to and from the brain.
Deep, dark shade is best for chickens to escape the heat. If you don't have deep, dark shade, make some. My girls spend most of the day lounging and foraging in the woods when it's really hot out.
Offer electrolytes in one waterer on really hot days so heat exhausted chickens can replenish their vitamins and such.
Bringing chickens into air conditioning for extended periods is dangerous because once they acclimate to an air conditioned environment, they become less tolerant of heat and more likely to get heat stroke once back outside, even if it isn't extremely hot. Bringing them into a shaded spot, like a garage, to cool down for a while with supportive care is better.