do you know the 40k basing kit from GW i use that for most of the bigger creatures or the better models. mostly i paste on plastic model filler smoothing it in a fairly thin layer over the base, and then taking a stiff short hair brush and stippling it. This has the effect of not only giving it a brilliant texture, thats better than sand in my opinion, but also gives it ridges and dips,that look natural, and keep it 3D. I then base coat over that with chaos black. then paint on scorched brown, then dry brush bestial brown, then dry brush on a little snake bite leather. I touch any stones ive added with codex grey and then dry brush fortress grey, then dry brush skull white. Then i paint the edge of the base chaos black, and glue on some small patches of light green static grass.
"Cheer up it'll get worse"