when I used to map, i used to use areas of 512x512 or 1024x1024 set at level 4 so u'd get a pretty large number of triangles to tweek, then set a high radius of effect and a low level of deflection for the displacements. then slowly raise/lower the ground in a roughly circular motion. I found that using this technique gave a more realistic effect for ground and rock faces than using small radius' of effect.
another thing is try and get pictures of something you want to replicate. often helps no end to have something to reference against.
o and small subtle changes always look more realistic than big ones, nature is more often smooth and flowing. rarely jagged and pointy cones