Mid_range pencils from brands like Staedtler or Faber Castel offer softer application, which allows you to get more color into the paper. This can produce a more vibrant color and reduces the chance of white flecks of paper showing through. Softer wax pencils are also better for shading and blending.
Get even! Producing a nice even color with your coloring pencil is all down to pressure. Push harder on your page for darker coloring, applying little pressure will producer a much lighter color. It is tempting to put lots of pressure on the pencil to produce the darkest color _ don't do it! Too much pressure will likely cause you to break your pencil leads, produce a scratchy finish to your coloring and give you less control. Instead, try applying your pencil with a little less pressure and use small circular motions with the pencil to get an even finish.