These extra sheet of paper will stop your coloring being affected by the texture of the surface you are working on. Colored pencils will easily pick up even the smallest dents, divots or wood grain textures. For smoother coloring give your page that little extra cushion! It is also useful to add paper between your page and the next when you are using a coloring book, the paper protects the design underneath from being damaged.
Use good quality crayons (Crayola works well) for the best results. Making the fill color darker around the edges is a good technique for adding dimension. As you work, don't press too hard. It's better to add layers of color than to have too much color that you can't remove. Take care to color evenly and without causing color streaks. When you're finished, place a piece of scrap fabric over the coloring and iron the paper on a high setting. This will heat set the coloring and remove excess wax.