Even with proper long lens handholding techniques it can be quite a challenge to get consistently sharp results with slower shutter speeds (a speed that can vary from photographer to photographer, for me that may be 1/500s. or slower with my 500mm f/4 II and attached 1.4TC). One easy tip that can yield you a few more keepers with static subjects is tripping the shutter for short bursts of 2-3 frames. It’s digital, no wasted film! In my own experience, when culling the images on my computer, it is so often the second of the short burst that is pin sharp compared to the first or third frame. Imagine I had only taken one frame each time, likely a softer one than the second that was not taken!
Chestnut-sided Warbler, male in breeding plumage, Canon 7DII + 500mm f/4 II + 1.4TC III, manual exposure, evaluative metering, 1/320s., f/7.1, ISO 800.