The process for correctly claying a vehicle is a very simple series of actions.
First, make sure to give the vehicle a thorough wash and clean all soil and dirt from its surfaces. Dry the vehicle and inspect the finish for any imperfections you can work on.
Before applying to the surface, remove the clay from the packaging. Preferably, break the clay in half and roll one half of the clay into a ball.
Next flatten the ball into a pancake — this will allow easier movement on the surface and better the quality.
Before starting, check the paint surface for dust and or debris. Even a slight breeze can deposit dust on the surface that, in turn, will cause scratching.
(from: http://www.carwash.com/articles/87621-all-about-clay-part-2)
