To achieve the airy and light appearance of a watercolour with pastel is fairly easy. Using white paper only, stroke with the broad side of your pastel stick across your paper (break it in half if the stick is too long). Vary the pressure using the darkest values first, lightest values last. Apply some of the light values directly onto the white paper and let the paper come through. Try layering complementary colours for a beautiful effect. Note: A disadvantage to this method is that the tooth of the paper fills up very fast and will not take too many layers as a result.

Coming from watercolour? In watercolour you work from light to dark, but in pastel, you are building from dark to light. If you have trouble reversing your thinking, try applying your light colour areas first and 'save' empty spaces for your dark colours. However, you must make all your decisions from the start because once you have applied light colours you cannot go over it with a darker value without risking the clarity of your colours.

When looking at the model while rendering a sketch or full portrait, the part you are looking at comes forward. Squinting helps trick our eye so we get the proportions better. Similarly, try looking just off to the side of what you are working on. That would mean working on an ear while looking at the nose.