A free AF fine tune method

Nikon has a guide for AF Fine tuning somewhere on their website.

If I remember correctly, they recommend setting a zoom at the mid point of the zoom range and then running the AF fine tune test and adjustments.

That makes sense to me if you plan on using the full range.  On the other hand, if you always use the zoom at the wide end or the long end, you might want to pick the mid point for your typical use and set to that.