There are many different answers to this question. You can do things like keeping them inside during extreme heat and making sure that your dog always has a full bowl of freshwater.
Consider how hot it is outside. If it’s hot for you, it’s most probably worse for your dog. If you are planning to walk your dog, it’s better to do so in the early mornings or afternoons, when the sun isn’t at it’s peak. You also have to keep in mind that dogs don’t wear shoes, so if the pavement is hot, it could potentially burn the pads of your dog’s paws.
Certain breeds experience the heat more drastically. Brachycephalic breeds like pugs, bull dogs and boston terriers have flat-shaped faces and can’t pant as well as other breeds. Long-hair dogs (or dogs that grow undercoats) will also feel the heat more than short-haired dogs, so make sure to keep them in the shade or limit their time in the sun. Make sure to take extra care of these dogs and keep them cool by keeping them indoors and making sure that there is good ventilation.