It also depends on what you are after. If it's illustration then I would say get good at doing everything in greyscale before you even touch color. At least that's what I get from the professional information I have been able to gather.

If you are doing maps then it may not be as important to do that.

My best skill is pencil. So, if I need something to look just right I will draw it on paper first. I include shading so it looks as good as possible. I'll go for a black and white photograph look if I'm really serious. Then I scan it in and go from there.

I'm still a noob when it comes to painting so I like being able to add color on the PC where I can remove/undo stuff I don't like. I would be having to toss a lot of canvas if I was doing it the traditional way.

I have also taken to drawing out my brushes (mountains, trees, cities), scanning them in, cleaning them up and turning them into brushes I then use to create a map. I did that with the Empire. (Which I just realized I never posted into the finished maps here. I guess I should do that.)