The main problem on texturing process I encountered was the bump while using lightracer. If you use lightracer you know what I mean, if don't take a look below.
A standard bump map with lightracer usually get this result:
Viewport default displacement:
rendered version of default displacement on the mesh:
Ok, Mixing both results is possible to achieve better results at the final render.
Now the texture preparation:
There is no secrect trick on preparation of the textures, you can easyly find some very good wall/concrete textures, buy some of the great 3DTotal textures or take some with your own digital camera. What will make the difference is the care when dealing with details and customization (like the door texture). As far as almost every project overview here inside 3DTotal covers nicely texture creation and preparation through layer blending, I'll show only few steps I used to mix these one. In many case you'll note that you should make a couple experiences with blending mode to find the desired result, according the color and darkness of the layers involved.
Ok, sometimes you can't see too much difference between some blending modes, it depends on the color involved and when dealing with gray tones you may find a bit hard to achieve color blending mode, my advice is to make several test with the blending modes on Photoshop until you get confortable, so when you need them you will find the effect you want more easily.
For the door tiles I used this shape a few times and then erased a little bit the down part to fade and get a more gradual mix
and then blend to the concret texture I prepared before
The final (diffuse)textures for the scene are:
The snake body I used a similar tile
and mapped to a shape near the body of the snake and rendered it. Then positioned the figure over the mapped region as show figure below and changed the blend mode to overlay.