Tell me how to achieve this...

That is some very clean painting
I usually just drybrush the regular rank and file models, but drybrushing will never look as clean as that.

From the looks of it the model have been given a dark brown base coat all over. He the basically just neatly painted the skin and scales with two separate browns. I'm not even sure he highlighted anything with a lighter color.

 

The example you have shown is pretty easy to achieve, as @Pinktaco has said, The hardest part is being neat.

1. Base coat in dark brown.

2. Paint the darkest of the tan colours, you can apply this to all the model leaving the recesse's showing the dark brown, where an area meets another leave a thin dark brown line.

3. Then apply the light tan on the areas you want it, painting the full model in the dark tan as your first layer will help in giving a nice depth for your lighter colour.

You can go further and highlight the tops of the scales and then glaze the bottom halve but the example has no highlights.

 

I would base them in balthasar gold, wash with Agrax and then reapply balthasar on the top half and then edge with liberators gold on the head and shoulder area, but it's alot of work for rank and file models most people do a decent job on rank and spend more time on leaders or monster models, but it's upto you how far you want to take them.

When you reapply the balthasar do it in an arch shape following the scale, sounds really hard but you only need a touch of paint.

Once your happy with your test model try painting 3 or 4 together and see how you get on.

 

Do it in gahenna's you can always repaint if you don't like it, I thought you had balthasar my mistake.

 

Base coat Liberators, Sepia wash, Layer with Liberators, edge with silver