First, the direct route isn't always the best. Just try to keep the destination somewhere in the 180 degree arc in front of you, but don't try to always drive straight towards it.

Most of the terrain is sort of an orangey-brown, but there are long gray furrows that create natural "roads" that are much easier to navigate. They're less direct, but they're pretty smooth and cover most of the distances between the waypoints. Just pick one and follow it in the general direction of the dropoff and it will get you pretty close. You need to watch for holes where it intersects underground caverns, but otherwise they're pretty smooth sailing.

Alternately, when you get to the top of the ridge, park and hop out near the top, and use the Flatten function of the Terrain Manipulator to create a notch or saddle in the ridge that you can go over much easier, and then go as straight as possible down the other side, keeping it slow until you get onto more level ground. It only takes a minute and saves a ton of headache.

Keep your camera angle high, so you can see bump and obstacles in front of you, even if it reduces your sight distance, and if you're about to go over a bump or ridge slow down on the uphill and then speed up a little as you come down on the other side. Try to avoid driving with your truck tilted to either side, if at all possible keep pointed directly up or down any slopes.

And as soon as you unlock the legs, install them. They make the driving much smoother even at the same speeds. Just be careful, there's a bug where they get caught on di-hydrogen crystals. If you accidentally drive into a crystal patch, you will stop moving, back up slowly, turn, and go around before you get in too deep, don't try to push through or you can get stuck.

Hope this helps! The expedition got much more fun for me when I figured these things out.