Four Ways: staying hydrated, staying dry, using a lubricant, and wearing appropriate clothing.

• Hydration: Drink lots of water before, during, and after your walk, run, ride, or other workouts. This will allow you to perspire freely so the perspiration doesn't dry into salt crystals that can enhance the chafing.
• Staying dry: Use an absorbent body powder, cornstarch, or potato starch to stay dry in any areas where you have crevices (under the breast, crotch, armpits, fat rolls). Look for unscented powders if you are sensitive to the perfumes often added to these products.
• Lubrication: Walkers, runners, and cyclists use a variety of anti-chafing lubricants to keep the skin areas sliding past each other instead of rubbing each other raw. Plain old petroleum jelly is the standby choice. You can apply it liberally before your workout.
• Clothing: Loose clothes may feel good on the trail and during workouts, but to prevent chafing you need a snug fit. Bike Shorts or Compression Shorts are designed to give a skin-tight fit that will prevent chafing for the lower body or thigh area. For the upper body, look for skin-tight tops, or Compression Garments if you get chafing under sagging skin or fat rolls. Pay attention to the fabric when choosing your workout gear. You also need to choose clothing that is seamless or has flat seams in the areas that are prone to chafing.