At the beginning of the mission, you will have to spend some time going east, because that's where Ngumba Industrial Zone is located. First, you need to reach the central part of the map and you can do it in two ways. Going through Munoko ya Nioka Station is quite risky, because you may be detected by enemies. A much better idea is to head north-east and find a mountain path, which is not guarded by anyone.
When you reach guard post number 20, you have to turn north-west. The next part of the journey is much more linear and has been shown on the picture above (you can "discover" it by collecting intel from guard post number 20; you will find more details in the optional objectives walkthrough).
Shortly after you walk away from guard post number 20, you will reach a smaller camp. You don't have to attack the enemies here at all, because you can go past the fence by going through the hill on the right. Head further east, going past guard post number 17. When travelling along the river, lay on the ground and start crawling as soon as you get close to new enemies (you can also neutralize them).
At the end, choose the north-eastern path leading to a large hill. There are 2-3 enemies here, but you can sneak behind their backs and use the thick plants to stay hidden. You need to reach a big tunnel leading directly to the Industrial Zone.