Get yourself a dirty wash - kind of grey/brown - and mix it with a medium flesh shade. Keep it thin. Then just brush it on in layers. The thinner the layers, the more subtle the effect and the more control you'll have in building up the effect gradually in the places you want.
Keep the shade deeper along the jawline and under the chin and/or in deep creases around the mouth, fading gently as it gets to the cheekbones. Remember a black haired person might be expected to have a deeper stubble colour (possibly add a little blue to the mix) whilst a blonde or red haired person will have a much paler colour.