When you are above the target, sweep in an "X" pattern as shown on the right.

As you sweep, note where the signal peaks or is most shrill.  

Adjust your "X" pattern sweep until the peak from each sweep direction occurs in the same spot.  

This will help you find the center of the target object.

On vertical objects, such as property pins, the peak signal will occur directly over the center of the pin.  

On horizontal objects, like manhole covers, the peak signal will occur at each edge.