DEFINITELY start with the clay bar, no matter what you are planning to do next.
It is amazing what crap gets embedded in paint while sitting in a garage, where one thinks their car is safe.
The clay bar will remove the impurities that you can not see, and leave the paint like glass. then you can use a medium cut compound adn a wool buffer to get the haze off. Once this is done, and the finish looks good, put on about 3 coats of wax and wax it 2 t o3 times a year, regardless of miles driven.
Be sure to use the clay bar treatment any time the surface is not as slick as glass.