1. Join a Clean Gym. The most important step you can take to ensure you stay clean and healthy at a gym is to join one that isn't dirty. When shopping around for gyms, make sure you take note of what the machines look like. Get a free trial pass and go more than once before you join. This will give you a good idea of how clean it is on a daily basis.
2. Wipe Down Machines. While you're at the gym, one of the best ways to keep yourself from coming into contact with germs is to wipe down the machines before you use them. In aperfect world, everyone would use antibacterial spray to clean up their own mess. Since you can't know for sure who cleaned up and who didn't, wipe down the machine before you use it. Once you're done, wipe it down again so you don't leave your sweat and germs all over the pads.
3. Gym Towel. Another way to minimize your contact with other people's germs is to bring a gym towel. Place it over the machine you're using so that you sit on the towel instead of the machine. You can also use it on the floor if you need to do any stretches or exercises and don't trust the cleanliness of the mat. If you do yoga, buy your own mat. Make sure that you wash your towel and mat frequently because they can turn into a breeding ground for bacteria.
4. Wash Your Hands. After you're done with your workout, wash your hands thoroughly with warm water and soap. This will drastically reduce the amount of germs on your hands.
5. Clean Clothes. If you wear the same shirt and shorts to the gym everyday, you need to change your habits. When you sit on a machine, the bacteria cling to whatever clothes you're wearing that day. The bacteria can start to multiply and if you wear the same clothes each day, they'll start to move onto your body and can make you sick.