There's nothing you can do to prevent a flat. Using heavy duty tubes helps, rim locks help, spinning the locking nut on the valve stem up to the cap helps, and most importantly - being prepared helps. I typically run between 10-12psi for the muddy conditions around here and don't adjust tire pressure up just because the trail conditions my have changed during the ride. Being prepared for a flat is no different than being prepared for a chain break and carrying a piece of chain, chain breaker, and two master links.

I always carry two tire irons, Slime Scabs, CO2 inflator, and "my little tool". Check out this thing at mylittletool.com.