Tension
Pulling the hair with tension as you dry it will make the style last longer. Curly hair being blow dried straight will need a lot more tension than straight or wavy hair. A large radial brush will help you to smooth and straighten curls but still create volume and movement. Ensure the tension is firm but without causing discomfort to your client.   

Angles
The angle in which you direct the brush and airflow through the hair will aid you in achieving root lift and volume where required. 

You should keep the brush on the base of the section if you require lift (on base), and drag the hair back away from the section (off base) if you require a flatter look.

Airflow
You must always ensure you direct the airflow away from the clients scalp to prevent burning the client and causing discomfort. Always keep the airflow moving, as keeping it in one area could cause damage to the hair and scalp. 

You should direct the airflow in the direction of the style to ensure root lift where required. Follow the cuticle direction, aiming downwards from root to point to follow and smooth the cuticle scales, avoiding disturbing the hair you have already dried.