Damn, I thought sadekey101 was asking how people do nice routes.
That, too. So here's my "secrets".
Vary the ground texture. That does more to affect how a layout looks than most other techniques. Find two or three similar textures, dial the circle down fairly small and sweep some texture across the ground. Keep mixing them up so your wilderness doesn't end up looking like His Lordships lawn.
Also, textures render from farther away than objects, at least on my computer, so if you have a forest, back it up with forest textures on the ground so it doesn't look like the trees just appear out of nowhere as you approach a bare slope.

o I've had that problem with my early efforts.)
Rolling hills are done by dialing the circle up big and the sensitivity down low and sweeping across the terrain.
(We do a lot of sweeping in this game. It's all good clean fun.)
Also, remember that the real layout usually looks good, but not as good as the pictures. We all pick and choose the best angles to make the best pictures we can.
For the rest, Colhad is right. It's like the directions to get to Carnegie Hall. "Practice".

Start small, one or two boards. Fail. Stop halfway through building a layout and erase it because it doesn't look right. Over time you'll find that fewer of your layouts get erased and some actually look good enough you'll want to upload them for others to play with. Let us know when you do.
Good luck.

Claude