After the scene is secure (if possible) call 911, giving a COMPLETE description of yourself, ask for A) the police and B) an ambulance ... YOU may be hit and not know it yet. Plus the bad guy (although he may not deserve it) might need medical attention, and trying to help him/her only makes you look better.
When the police arrive: Give them a BRIEF synopsis of what happened, factual, to the point and include your fear of serious bodily harm/death. THEN EXERSIZE YOUR A) RIGHT TO REMAIN SILENT AND B) A LAWYER (be polite about it though, let them know you WILL talk AFTER speaking with your lawyer).
You WILL be detained and depending on how FUBARed the situation is, you MAY be arrested (long enough to be questioned by Homicide, the Shoot Team, Special Investigations, or whoever investigates shooting in your city/county) ... KEEP YOUR COOL ... We (the Cops) don't have a magical crystal ball to tell us who is telling the truth, so just be patient with us.
I know of one shooting where the bad guy came to the door of the ex-girlfriend and pulled a Tech-9. The NEW boyfriend answered the door and when he saw the weapon, grabbed a 9mm of his own and opened fire. Bad guy, who forgot to take the safety off the Tech-9 goes down with multiple torso hits without firing a shot. The new boyfriend was "arrested" while homicide (the BG didn't die, homicide just happens to investigate the shootings here) gathered up all the witnesses, took statements and examined evidence. The new boyfriend was at homicide until about morning, then released without charges, The case was sent to the Grand Jury who gave it a No Bill (no charges to be filed) and the case, now ruled self defense, was dropped.
The only other advice I can give is what a veteran cop with about 7 shootings while on the job told us to do if we ever got into a shooting, "When you're up there with your union rep (lawyer) TELL THE TRUTH, PERIOD." Don't add lib, don't guess, speak of only what you knew or believed to be true AT THAT POINT IN TIME. If you were so scared that you almost (or did) wet, or drop a load in your pants say so.
You may want to babble ... don't, if your lawyer says shut up, then shut up.
You will be asked the same questions over and over. You will be asked to "run through it one more time" several times. That is why it is important to tell the truth, if you tell the truth, it will be easier for you because you won't have difficulty remembering what you said the last time they asked you the question and your story will remain the same ... always a good thing.