Increase the Water Intake:

During the monsoon you should drink plenty of water to your body hydrated. As you don't sweat so much during the monsoon season, drinking more water will drain your body heat and other toxics.

Keep the mosquitoes away:

With the monsoon come the mosquitoes! Water stagnation and pooling during the monsoons provide ideal breeding grounds for mosquitoes. Make sure that the area surrounding your house doesn't become a breeding ground for mosquitoes.

To avoid mosquito bites, expose as little skin as possible especially in the evenings. Or apply repellents to ward off mosquitoes.

Personal hygiene:

Maintaining personal hygiene can help prevent most of the common illnesses that occur during the monsoon season. Wash your hands as much as possible. Keeping your hands clean can prevent the spread of contagious diseases, like colds and flu, which are rampant during this season.

Shower after being caught in the rain as this will protect you from many infections.