Most modern studio lit and sanitized textures these days are incredible flat and boring because people think they should rather rely on shaders and fancy lights  to get "correct" results.

So, what momodot said: Start with an "old" texture with lots of tonal variation and burned in  highlights which was made before we had the wonders of IBL-light and 200-node skin shaders.

The Z-Toon technique might also help to get a painterly look.
(See pic)