When approaching a large rock, put a tire on it rather than trying to straddle it, or you might high-center the truck. Drive slowly in 4-Lo but with enough throttle to maintain momentum. You'd be surprised at how much suspension travel your 4x4 actually has--most people panic about rolling without giving the suspension a chance to articulate.
Remember, don't try to drive over an obstacle or trail that makes you uncomfortable. And don't feel embarrased about asking someone to spot for you. Even those with many four-wheeling notches in their belts need help once and a while. If you feel like you need a helping hand or just a refresher course, sign up for an off-road class such as EVOC's. The best way to gain experience is to learn from the experienced.