makes sure you have the block thoroughly cleaned of all dirt grease and grime. its good to either pressure wash it down with a strong engine degreaser first. I like to use carb cleaner after I do that with a stiff brush, then I wipe it down several times with a good prep solvent and let it air dry.
Personally I just use the dupli -color straight out the can, light coats until I get a smooth consistent color coat. Whether you like to use clear on top of the color I believe is personal choice. I never use the clear unless its a trailer queen.