I always suggest doing what the old masters did in their apprenticeship : seek out a master (lots and lots of images and museums on the net), choose a half-dozen of her/his images that you like best, and do your best to emulate them in your chosen software. Van Dyck, Rembrandt and all the rest spent 10+ years doing this, and even when they had become masters in their own right, they continued learning from others. The mature Rubens, for instance, was once sent to Spain as an ambassador (he was a diplomat as well as a painter), and spent many, many hours copying Velasquez' paintings in the royal collection. If you like battle pics, I'd have a look at Lady Butler's napoleonic battle paintings, and perhaps at the movie "Waterloo" (available on DVD). Have fun.