They begin by finding a group and following them. At first the chimps run away, and the researchers do not follow. Gradually the chimps allow the people to come within sight and not run away, and slowly over time, allow them to come within 10 feet or so. These chimps recognize CK, the FA who took us out. When we first saw them, they got up and walked away when I looked at them, but after a couple of times, accepted the newcomers as part of the 'human community'.
Every effort is made to simply be an observer, part of the landscape.
If you want to eat your lunch you have to walk away so they cannot see you - they might start thinking that the humans have something more interesting to eat than what they find themselves in the forest. At one point CK told us that he thought they were going to go to the village to raid banana trees. They don't eat the bananas, but just the stems, which kills the trees. The people don't like this, and chimps have been killed. Well, we waited an hour at the road, watching, talking with the folks passing by.