Yea practice makes perfect. Your on the right track. There isn't much technically speaking "wrong" with the second rock pic you posted. Its just preference from there; experience too, being able to convert what you see in your mind as a rock, onto the computer.
You want to keep brushes on powers of two. 2,4,8,16,32,64,128,256,512,1024,...,... . We do this for a few reasons
A) The engine VVIS process cuts the map up every 512 units.
B) Textures are designed and aligned for these units.
C) When you displace an entire map, it is easy to "sew" different brushes together when they are on these powers. You can have one brush at 512 units, and the other at 1024 units and "sew" together (assuming the vertex points align on one face).
D) In the most general concept, the game has been designed to work best with these 2^2 units
If you want to add a clear displaced path for a player to walk on, learn to use the "vertex manipulation (VM)" tool. Basically create the brush, displace the 2-5 sides (including the top) and keep the displaced brush a box at the moment. From here, Go to the VM tool and depending on how you built the map, look though the Y or Z axis and drag the top two vertices, vertically/foward and back, until you can align it with the cliff face next to it.
Sorry I could not get into extreme detail, I am Chocolaty wasted. (well, Post-Chocolaty wasted)