Cover Your Head
Make sure that you have your head covered with a p-cap or a floppy hat as you work in open areas. This will protect you from the direct heat of the sun and although the difference it creates may not be noticeable, it will certainly save you greatly from a direct exposure to the scorching sunlight.
Wear Breathable Clothes
This is also very important that the clothing you wear is made of breathable fabric to allow the inflow of air. This will keep your body reasonably cool and you will feel great whenever there is a bit of breeze blowing across.
Drink Loads of Water
Heat can cause dehydration so make sure that you drink a lot of water. Since you will be sweating a lot, make sure that you drink at least fifteen glasses to counter the loss of water in your body. It is also not a bad idea to drink lemonade as it will provide you body with energy as well. Make sure that you also consume drinks that offer essentials for the body as sweating does reduce some important salts in the body.
This will not be easy while you work but you and your coworkers will have to take turns and everyone will need to take some rest during the day. It can be as simple as sitting under a shade where the heat is less. This will allow you to cool down and let your body feel fresh. If you have the facility, take a shower, it will be a big help and will keep you cool.