Just posted this in a thread in the help section and thought it could be useful for people to reference to. The most important thing to keep in mind is to keep every major object or portion on a separate layer during the drawing phase. You don't have to, but I would greatly recommend it. The more organized you are the easier it will be to make changes if you have to or want to.
Here's a background I drew for a game I was working on not too long ago. These steps aren't in the order in which I did them, it's just to give you an idea of how you should go about drawing these things.
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Even now, there's so much I would change or do differently if I were to redraw this background. Each one is somewhat of a learning experience. You only get better if you keep practicing and trying new things.