1. Colour everything else BEFORE using pastels. They should always be last as they smudge something terrible!
2. Use a fixative to 'set' the pastels. Cheap hairspray works great.
3. Apply the pastel in small circles. Applying in lines will not trick the brain into seeing a seamless blend, which is what messy circles achieves. Also, it gives a really cool cloud effect :)
The materials I used in this video are: