On my Nissan 240SX the paint was not in good shape when I first bought it. about 4hrs of hard labor nad its like new!
I used a 3-step process by Meguiars.
Step 1) Body Scrub - went through quite a few applicator pads really scrubbing some of the stains. $5 at Pep-Boys
Step 2) Polish - Polishing went quick. $5 at Pep-Boys
Step 3) Gold Class Paste Wax - Gives a long lasting deep shine. I prefer the Paste over the liquid. $10 at Pep-Boys