While there is no way to stop your goggles from fogging 100% of the time there are three options that offer differing levels of success. Option 1. Use a little dish detergent on the lense then wipe it clean. This will help some.
Option 2. Upgrade to a thermal lense for your goggles. These are available at the Back Country Paintball Pro shop. The thermal lense works just like the thermal windows in your house there a two lenses that trap a neutral layer of air between them that helps prevent fogging.