1) determine if you need to clay the car: after washing and drying, run your fingers over the paint. it should be smooth, if it has particles, claying might be needed. claying can also remove oxidation and watermarks.
2) if you need to clay, prepare the materials. Mothers has a good claying kit that has the following:
-Quick Detailer (for lubrication
-clay bars
-MF cloth
so for claying itself...
i) ensure the car is dry
ii) knead the clay into a form that you can easily rub across the paint, ideally it should have a flat surface
iv) spray the QD onto the surface
v) rub the clay across the surface with the QD
vi) wipe with the MF
now... you have to check the underside of the clay if it has a lot of dirt... if it does, knead the clay again to expose a clean area.
repeat it for all panels
just remember to store the clay in an airtight container to prevent dessication. the lock n lock containers work quite well