At Grinding Gear Games we use a technique called Tile Based Texture Mapping in order to make good looking ground.

http://pathofexile.com/news/2010-12-20/tile-texture-mapping

There isn't much online about creating art using the technique so our lead artist thought he would create a tutorial for his process when creating ground textures.

There might be a few other tips in there that apply more generally as well.

Hope someone finds this useful.