The North Carolina Zoo is a large, sprawling zoo with two entrances. Having a plan for your visit is crucial. Don't just let the zoo happen to you. Study the map and plot your strategy.
If the kids are dying to see elephants, plan to start at the "Africa" entrance. If polar bears are a top priority, park near the "North American" entrance. There's a lot of ground to cover, so if seeing something specific is important to your zoo-visiting crowd, plan ahead so nobody is disappointed at the end of the day.
Speaking of a lot of ground to cover. Comfortable shoes are obligatory. If you're bringing young children, even if they insist they've aged-out of their stroller, bring it. The walking paths are easy to follow and shaded for the most part, but there's a lot of walking to be done. You don't want to set the young ones up to fail. If walking is a challenge, there are shuttles available.