Of course there is no guarantees, even in a state like Florida which has very favorable laws but I believe if you use common sense you give yourself the best chance.
Is the threat real? A good shoot is against a real threat not just paranoia, however don't delay in making the decision, just be as certain as you can be
Do you actually fear for your life? If not, do you have a less than lethal alternative, if you do think about using it instead, but again, don't delay in overthinking it.
Can I retreat? Even if you have a no duty to retreat law like Florida, if you can get your butt out, DO SO. This is not the place to think macho, if you can run, run ... NEVER, EVER, EVER PURSUE ANYONE ... you are not trying to catch a bad guy, you are not LEO, you are only trying to protect yourself and those around you
Tell the truth. Don't try to make up a favorable story when questioned by LEO, just state EXACTLY what happened, in the order it happened as accurately as you remember it. If you lie, your story will fall apart and come back to bite you. If you can ...delay the interview until you are more composed, ask to go to the hospital to be checked out that will give you some composure time. Even LEO are usually given 24 hours before debreif after a shoot.
Keep the number of a gun savy attorney on you and give them a call ... representation in the legal system is never a bad thing. Tell LEO you prefer to have representation and then shut up.
Of course, we all hope that we never have to worry about any of this and never have to use our weapon, but if you are so worried about the aftermath that it affects your judgement, then don't carry. In most cases of good shoots, the law does wind up on your side. Work in your state to get better "self defense" laws. The new Florida "castle doctrine" law has been working very well since it has been in effect, try to get your state to pass something similar if they don't have one.
Best of luck ... Be Safe!