Soft Pastels are interesting media to work with. It can also be fun for you can use your own fingers to apply the color or you can use a brush or cotton balls.Just outline the drawing with your chosen color and smudge it with your finger, brush or cotton. You can achieve a soft, hazy look with this just like the one in the picture. Plus, you can actually erase smudges using eraser.
Use Crayola. These are the best and have the best color saturation. Use a paper that will grip the color evenly. I like Stonehenge or illustration board. Have a good hand_held sharpener handy. Always try to keep a point on the crayon. This makes it go on more evenly. Apply the crayon in a professional manner. Just like you would any other fine art tool, use control and be deliberate. Don't become five years old again!