I would use rubbing compound only as a last resort. I would use a clay bar kit first.

Clean with soap and water to remove old wax, grease, etc. Further remove bugs, tar and stubborn stains with bug and tar remover. After is is as clean as you can get it then use a clay bar such as Meguiars and then see how it looks with a coat of wax.

It could also be sealed with one of the newer sealants such as Wolfgangs and then waxed but might not be worth the trouble.