Before you use a wax or sealant, you may like to prepare (or 'prime') the paint… pre-wax cleansers and polishes remove dirt and watermarks left over from the wash stage, remove oxidisation and light swirl marks (especially if a machine polisher is used) and also enhance the finish through the action of glaze oils.
Lime Prime is one such product, and arguably 'best of breed' after having won Detailing World Polish Product of the Year back when it was launched in 2010. Supremely workable, it can be hand or machine applied with a little going a long way. It uses fine cut diminishing abrasives to gently hone the paint surface without troubling tough, modern clearcoats. And it smells limey, if you like limes.