Follow the road here. This is a short section, but a tricky one as well, because both In Guezzam and Assamaka seem to be surrounded by sand. Get some speed in order to 'float' over the softer regions. The customs at Assamaka can be picky about where you should park your car. There is no road here, only markers showing the way.
Tracks run in almost every direction, so it's easy to get lost.
There are a few sand seas you may get caught in if you venture too far on your own, especially when closing in on Arlit. Otherwise the terrain is rather hard and hilly. Some sand dunes can look very soft but actually be quite hard when you drive on them. The road is very good. It seems that some places will be submerged in water during the rainy season.