Interesting to see the number of folks pontificating knowingly that have never had to face a gun, in all probability.
Psychology like strategy applied to a gun fight usually goes to Hell in a hand basket as soon as gun(S) IS/ARE drawn. Most fatal gunshots and successful gunfights occur within 12 feet. Outside of that range you stand a tiny bit better than average time of successfully evading and escaping. Having said that, I side with whomsoever said, be careful about getting in those situations. An ounce of prevention is worth a pound of life. And I can't imagine that you carry so much money or drive such an outrageous car that any of it is worth your or a loved one's life.
If you find yourself in a situation where you face a gun, and all things are normal (whatever that may be in this situation) ... You have approximately 1/12 of a second time advantage, which used to be called the "Initiater's Advantage". That would be the time between the moment you initiate a move and the fact registers in the attacker's head, and he begins to respond. Fancy stancing and crossover stepping should probably be about the last thing you think about... And you need to train in a realistic fashion.
There is a well respected gentleman named Massad Ayoob, I believe, who has written extensively about survival in these types of situations, complete with pictures. You might want to think in terms of consulting his books as he is, or was, perhaps, taught extensively, in survival courses and self defense courses.
Kenpo has the things you need in it to effect a survival situation. Whether it is successful or not is a whole 'nother issue with many, many variables thrown in... Not to mention "luck". There is probably no template, or boiler plate technique that will work in all situations.
Dan