I have had the best luck with a four step procedure using Meguiars's products:
1. Wash car and use a clay block and detailer spray to remove embedded dirt
2. Apply cleaner using random orbital buffer; wipe off.
3. Apply polish using buffer; wipe off
4. Apply wax using buffer; wipe off. For this last step, I use a 3M liquid product containing UV blocks.

Meguiars makes a 3-step kit that takes you through all the steps. You need their clay block in addition to the waxes. The whole procedure takes about an hour on my 940.