Be Bold With Base Colour
I have only just started experimenting with pastels but have found that the more generous I am with the initial base colour, such as flesh tones, the better my picture turns out.
The 'rich' base enables the detail to stand out more and therefore I find it easier to blend as there is 'plenty' to go at. Basically, don't be afraid of pastels.
Spray your work when you feel you have achieved a near likeness, leave it to dry and go back to it to 'touch up' when you feel inspired again at a later date. Keep experimenting for the finish and look you want to achieve.