Things like points, divots, Certain lines or trees,caves, snow and running water.
Next is the rocks themselves. One thing i see people do a lot is just buy a big rock and put it in the tank. Theres no thought in that and it does not create a natural feel and takes away from the movement and shape or the rock. Why are mountains so amazing to us? Its because they are not a big slab of rock. They have all sorts of movement and depth. Things like points, divots, Certain lines or trees,caves, snow and running water.