Fastener companies which make fasteners, such as ARP, suggest that some type of lubricant be put on the threads before trying to accurately measure torque. Doing this cuts down on the amount of torque simply required to turn the nut or bolt and permits a more accurate reading. ARP recommends thread lube, which I think is like white grease, but I've used 30W motor oil. This is particularly important when dirty threads are involved, such as with a lug nut.
The points about a "clicking" torque wrench and unloading the spring are very good. I trashed my old "bar" style torque wrench for a Craftsman model some time ago and it works great.
My references say that for '68 through '82, the lug nuts should be tightened to 80 ft-lbs. Any more than that is overkill and could make the nuts too hard to remove for a flat tire on the road.