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.
Color Outside the Lines Sometimes. In some circumstances, like this one, you can color outside the lines because you'll cut the piece out afterwards. This allows you to use large consistent strokes, as you can see in the red kidney above and on the right. This is an especially helpful tip for younger students who are coloring the organs in this My Body project. (Just be sure not to use this tactic on the upper half of the heart in the My Body book because we won't trim around all those veins and arteries.)