First step is to avoid exercising during the middle of the day. Move your session to early in the day or later in the day but avoid the 11 am to 3 pm period when the temperature reaches it's highest point. Keep an eye on the weather report for the temperature and amount of humidity since humidity can keep your body from cooling itself properly.
Next, always stay hydrated by drinking lots of fluid before, during, and after your workout session. In fact, it is recommended that you consume 16 to 24 ounces of water about two hours before you begin your workout. When exercising continue drinking fluid and keep sipping liquids as you cool off. Stick with water or a sports drink while ignoring soda, caffeine, or alcohol since they can dehydrate you further. Do not wait till you feel thirsty because by then it's too late. In addition, forget taking salt tablets because the addition of salt can make you more dehydrated. You also do not want to drink real cold water because it can cause cramps.
It is extremely important to use a broad spectrum sunscreen with an SPF of at least 30 when you are outside. Make sure you reapply the sunscreen every two hours or if you sweat because the sweat may cause your sunscreen to disappear and you don't want to get burned.
When you get dressed to exercise outside, wear lightweight clothing that breathes. If you have clothing that includes some polyester, nylon, or lycra, the material will absorb any sweat making it easier for you to stay cooler. If you are going to be working outside, wear light colored fabrics that reflect the sunlight, leaving you a bit cooler. In addition, wear a hat to protect your head and if you are beginning to feel hot or tired, wet the had down so you don't get overheated.
Know your limits in regard to your fitness level. If you are just starting out, you will react to being in the heat in a different way to someone in great physical condition who regularly workout in the heat. If at anytime, you feel tired, nauseous, or dizzy, immediately stop and take a break in a cooler location. Make sure you give yourself time between each session so you can recharge your batteries and are in the best shape to exercise outside. Look at using a drink with electrolytes as you work out. This type of drink replaces salts and minerals you lose during your exercise session. Look for a version that has less sugar for the best results.
Finally, create a workout plan such as a short workout of speed walking in intervals, or choosing to walk up and down several hills. If you are doing intervals, extend the periods of rest for better recovery. As you work out more in the heat, you can extend your sessions. The other thing to remember is to monitor yourself to make sure you avoid heat related illnesses.
If you are a walker, many places have malls that open well before the stores open so people can go there and get their exercise walking before the crowds. If you do not want to exercise outdoors or have issues with the heat, look at the local mall. When I lived in Texas, I did a lot of speed walking in the local mall so I wouldn't overheat. Let me know what you think, I'd love to hear. Have a great day.