This surely differs depending on the perspective of your story and your writing style in general.
The best advice I can give you is: Try.
Try to write how you imagine that would "feel" and/or what you would pay attention when and how. The most commonly used point of view (I've been told) is third person, past tense.
It could be as simple as:
"John hit the ground, and immediately got back up, only to find that his
body was still on the ground, below him."
or, you can get into the mind of John as it happens:
"John hit the ground. The piercing pain from the bullet seemed to
slightly fade away as his body crashed onto the concrete surface
Unsure whether feeling the blood leaving his body, or simply reacting
to the trauma of getting shot, he felt a certain lightness in his
Well aware that the shooter was long gone, he decided to get back up
and seek medical attention, and to his surprise, he got up easier than
ever. No pain from the wound or the uncontrolled fall, no resistance
from his clumsy and lazy body as he rised. Is this what adrenaline does?, he wondered.
Once upon his feet, he realized the reason that he had risen with such
ease; He was now looking down on his own body, still lying on the
ground in a large pool of blood."
These are just examples. We don't know your characters, your P.O.V. or your story, and I have no experience writing such scenes, but use your imagination and try.
For most writers, the difficult part is actually writing something. You can always re-write - but you can't get useful feedback on something you haven't written.
Another tip, is to research the thousands of people who claim to have had out-of-body experiences. I'm sure there are lots of content to get inspired by there.