You can see through the viewfinder the exact depth of field or outfocused area. Just before you press the release button, try to make sure that the focusing is still correct. Request the people around you not to walk about. The tripod is very important, especially if you're doing an extreme close-up. It should be as sturdy as possible.
Some professionals test the steadiness of the ground with a cup of water on a table.
If the water moves, you'll know the tripod is not on firm support. Or you can use the Nikon Bubble Level. In order to prevent wind-blown movement, surround your subject with a paper or vinyl wall. For extreme close-ups, always use the Nikon Cable Release.