Shown here is my technique for handholding the Nikon P1000 at tis full 3,000mm EFL.
Fingers supporting the end of the lens with thumb on the 'snap-back zoom' button.
This also puts the thumb in close proximity to the control ring for changing
exposure compensation on the fly if one is shooting AF or focus if shooting MF.
Using the 'sniper' position would be more stable, but then those controls couldn't be accessed.

Photographed at Smiths Falls, Ontario, Canada.