Offering a simple SHORT statement saying ONLY that you feared for your life and that you want to talk to your attorney is good advice, generally (ie, "I though he was going to kill me/my wife/my daughter/my son" and "I want to talk to my attorney.")
Pre-arrest, pre-Miranda silence (and post-arrest, pre-Miranda silence) has been used against Defendants in self-defense homicides before. The prosecutor asks, "if the Defendant was really in fear for his/her life and acted in self-defense, why did he/she fail to tell the police about it until days/hours later, after speaking with an attorney?" The prosecutor suggests that it's because there was no such fear and the killing was not in self-defense at all.
My Criminal Procedure professor joked that he would give his clients "Reverse-Miranda" cards that they could simply hand to the officer(s). The cards read "I want my attorney, Mr. ________________, Esq." The client was instructed to say absolutely nothing.
If you don't have any reverse-Miranda cards, then you may wish to simply say "I want to speak with my attorney," and then keep your mouth shut. Once you have invoked your right to counsel, no further questioning may occur until you have been provided an attorney or until you waive your right. Though it may be helpful in many situations to state that you feared for your life or that you feared serious physical injury, the safest route is probably to say only that you wish to speak to an attorney.
Remember, though, that investigating officers have common sense too. If they arrive on a scene and find that a young mother with a small child has just shot a large menacing-looking man next to her car in a dark parking lot in an area known for attacks on defenseless women, they will probably not try to twist her statement that she feared for her life into something else. If you are the large "menacing-looking" man, however, you've got serious problems.