A billion posts on this already if you use the search section... best clays to use are the medium to light ones for normal purposes. The Sonus Green clay is good for detailing, the grey ones good for slightly heavier work.
For beginning with, get a decent shampoo (I like Chemical Guys Extreme Body Shampoo from Car Wash n Wax) then Autoglym Super Resin Polish, followed by Autoglym Extreme Gloss Protection for protection. You can then get a wax for a bit more protection and to improve looks.