Hi guys,
so i'm developing a top down game at the moment and i'll try to create tiles for the environment now. I like the artstyle for now but i struggle with the rock/cliff tiles. They just look boring and don't fit the style very much. I looked at tons of reference images but i don't get it. Has anyone a tip or a special technique for how to create stone-like environtment. I don't know how i should do it with such a simple and limited style to fit 

thank you all!

(don't know excactly how to post pictures directly so here's the imgur link, sorry )
http://imgur.com/a/PJlwk