Find an office park that is closed on the weekend, but that has "streets" and stop signs, etc. Is your car a standard or an automatic? Have him practice three-point turns, have him practice parallel parking - even if there are no other cars around, you can snag a couple folding chairs to bring with you to set up as "practice cars" to park between.

Most of all, be patient. Try not to talk a lot, that gets distracting. When you are out of the streets for real, keep to side streets with very little traffic at first. Tell him when he does something well, not just when he screws up.