There is a lot of good advice in the previous posts. Let me add an LE perspective (Arizona Based).
Consider: Drawing "too early" can lead to legal ramifications, however "drawing too late" can lead to physical ones. This is an exigency you will face in a self defense situation.
A taxi driver in a southern Arizona city picked up four men from a club on the south side of town. The driver was in his late 50s, and a new CCW holder and carried a Smith & Wesson Sigma in 40 with the post 1994 AWB 10 round mags. He was originally from New York (retired NYC employee) and as such new to the whole idea and lifestyle of carrying a defensive firearm.
He took the men to their destination, a small rat hole apartment complex, and they declined to pay him. The driveway to the complex was a tight cul de sac, and driving away forward was not an option and at least one subject was behind the car, and the driver didn't have any idea that he could simply put the car in reverse and SLOWLY go backward until the subject moved or got run over.
When the driver picked up his cell phone to call 911, he was dragged out of the taxi and all the men put the boots to him. He balled up on the ground and took a vicious beating from the four subjects. The beating he took made the beating George Zimmerman took from Trayvon Martin look like a Romper Room tussle.
911 was called by another resident of the apartment complex who witnessed the incident but "didn't want to get involved" as the subjects were feared in the small apartment complex in which they lived. I was the second officer on scene, arriving seconds after my beat partner. We exited our vehicles and my partner assessed the condition of the driver, I had dispatch roll an ambulance and covered my partner while trying (unsuccessfully) to make phone contact with the resident who called 911 initially.
The smoke eaters arrived on scene and got the victim stabilized and onto a gurney and we were able to get a statement from him. The upshot was that he had no idea about disparity of force, or that the mere act of attempting to physically remove him unwillingly from his car was justification (This falls under carjacking and a good prosecutor could make a case of illegal detention or even kidnapping, as such is specific justification for the use of force in AZ).
When I asked him why he didn't shoot, he said "I didn't see a gun and my CCW instructor said that I could only pull my gun if they had a gun".
***?
I am not going to dissect all the ways in which the so-called "instructor" helped to get this man beaten into the ground when he could have acted legally and morally in his own defense. The point is that because the driver got bad information (I can't call what he received "training") and he waited too long, and in so doing was ultimately unable to defend himself against a clear cut case of disparity of force and took a beating that placed him in immediate and otherwise unavoidable danger of death or grave bodily harm.
The point is, he waited too long to act in his own defense, and was then rendered incapable of doing so. Once hands were laid on him and the intent to remove him physically from the taxi was made clear, he had every right to access his pistol and fire. He had bad/no information on this exigency, and took a terrible beating because he was afraid of prosecution.
The Arizona statute that clarifies Defensive Display was still fifteen years in the future, but had he said "I have a firearm and will defend myself, back off!" and drawn the gun, he still would have been justified once the intent to harm him had been made clear to his reasonable belief, or threats from the group had been made. I certainly would NOT have charged the driver with ANY crime. At the least, I could have charged each member of the group with Threats and Intimidation, and Criminal Menacing, as well as Theft of Service. None of those crimes are justification for use of force, but the totality of the circumstances would lead a reasonable person to believe that they were in immediate danger, and there is your justification to draw and articulate your intent to defend yourself.
After the ambulance left, we were able to make contact with the initial 911 caller, and she told us which apartment the men shared, and that they were landscapers and always left at 0500-0515 in the morning. Our patrol sergeant decided we would come back and hook them all up when they left for work. My beat partner and I went back to the complex at 0440, and other units positioned themselves on the street. When the lights in the apartment went on at 0445, four other officers including our sergeant converged on the complex and when they exited their apartment they were all taken into custody without incident. They were all tired, hung over, and bleary eyed. All four were charged with multiple felony counts. A search of their apartment incidental and pursuant to arrest revealed a small amount of marijuana and cocaine (only enough for a simple possession charge) and a stolen pistol.
The subjects were Mexican nationals, and were here illegally. The case never went to trial, they all took a plea bargain, did 18 - 24 (I don't recall exactly) months in state custody and I assume were deported after their sentences were completed.
I gave the victim the name of a GOOD instructor. As far as I know, he did return to driving a taxi after he recovered from the beating.
Don't wait TOO LONG to draw. Use common sense, and be able to articulate why a reasonable person, knowing what you knew at the time, would do the same thing.