Keeping a pet cool in summer? No sweat. Literally. We sweat to keep cool, the water evaporating off our skin cools us. Dogs, unfortunately, don't have that option. They don't have the same sweat gland dispersal as we do, so instead, they pant.
Keeping a dog cool in summer means that we have to keep these two things in mind. We need to let them pant (be especially careful with dogs that have flat faces, or when using a muzzle), and we can help them "sweat". There are a number of ways to help a dog "sweat". We can spray them with a water bottle, we can dress them in an evaporative cooling vest, and there are bandanas that you soak, or even freeze. These can give the dog a sweating action that they don't naturally have.
Dark coated dogs can absorb heat, so keeping them out of direct sun is very important. On the other side, light coated dogs can get sunburnt easily. Walk when the sun isn't beating down, or use one of the many places where you can go walking in shaded areas, try to stay to these for exercise on sunny days. Shaded areas have an added benefit of the walking surface not being blistering hot. If you won't walk in bare feet on a surface, please don't make your dog do it.
Proper grooming is as important in summer as it is in winter, and keeping the coat in top shape means it can do its job properly. Some people shave off double coated dogs in summer thinking that it makes the dog cooler. That can be the case, but it also makes them more vulnerable to the sun, to mosquitoes, and to cuts and abrasions to their skin which is normally protected by a thick coat. Better than shaving is a "carding out" of the coat, which is removing the dead undercoat (that fluff you see everywhere when they shed) and a trim. When done properly by a professional groomer (using high velocity dryers and coat king tools), this can actually keep a double coated dog cooler and safer than shaving it.
I know there is probably no need to remind everyone about pets left in cars on hot days, but just in case, please do not leave a dog in a car unattended. It can take only a few minutes for a car's interior to reach lethal temperatures. Even with the windows cracked, it gets hot in there. Using the remote starter to keep the A/C going sounds like a great idea if you're going to be 2 minutes, but most have a timer shut off, and if you get delayed in getting back to the car, that can lead to disaster. Just don't take the risk.
Hydration is essential, for both you and your pet. Lots of water helps keep everyone cool and able to fight off the heat. Dehydration causes systems to shut down, and makes everything the body does harder. If you are wondering if you or your pet has had enough water, your probably haven't, drink a little more.
The easiest way to beat the heat is taking advantage of the time of day when it isn't a concern. Early morning walks, or late evening. The sun is out a long time, take advantage of that. When the sun is beating down dangerously, stay indoors and relax in the A/C. It's OK, your health and your pet's health is worth it.