Half the Work is in the Reference
A quick post to highlight how important it is to find good references. It is not just about 'finding a horse,' for example, but more about 'finding a horse with a pose that works aesthetically in art.' A strong reference can give you 50% of the work already done. I am sure Chris already mentioned this, but if you choose a portrait with the right lighting, you are already halfway there. After that, it is just about applying your theoretical knowledge to the rendering.