Along with the above, don't overlook the simple measure of taking a piece of cotton saturated in alcohol to clean the lens contacts inside the F mount of the body, and on the mount end of each lens.

I do this a few times a year. Very low voltages run through those contacts, and drive focus, while communicating aperture, metering and distance data to the camera computer. So any electrical resistance is bound to throw things off.

Visit my Nikonians gallery.