My paintings are done with acrylic paint on canvas. I love working with acrylics because they are so forgivable and mistakes are easy to cover up.
As with most paintings, the background is important for setting the mood and is easiest if painted first. Using lots of bright colors and avoiding mixing black into your palette is a good way to get a vibrant backdrop for your dragon. Once the background is dry, you can use white to outline the shape of your dragon and get it just right before you begin to add color and depth.