We naturally picture fighter pilots during WWII getting into a thrilling dogfight every time they went up in the air, but I'm going to guess that was probably not the case.
What percentage of American WWII fighter pilots ever actually fired their guns in anger at an enemy fighter? Would most missions have actually been uneventful? What percentage of dogfights actually ended in one plane being shot down, rather than one simply disengaging and retreating? Was a pilot more likely to die as a result of an accident than being shot down by an enemy pilot? Was it more likely to be shot down by flak than another fighter?
What about say the gunners on board a bomber? I guess I am just looking for statistics mainly to get a better sense of what was "normal" for pilots and air crew during WWII, as opposed to what was sensational and what we see on TV.
What percentage of American WWII fighter pilots ever actually fired their guns in anger at an enemy fighter?
I'm going to commit a venial sin here and cite Lt. Col. Grossman's book On Killing. I'll avoid too much backstory here, but his uncritical use of SLA Marshall's infamous firing rates study is kind of controversial, and calls into question the greater accuracy of his work. That being said, his numbers for aerial combat I believe come from a more reasonable evaluation of war records and credited victories. In the book, he posits that one percent of fighter pilots were responsible for nearly forty percent of all aerial victories, and over half of the pilots had no victories to their credit. Whether this is indicative of a lack of desire to kill as Grossman goes on to state is another matter.
His argument is that most pilots went up there, flew around, shot at no one, and came home, letting the eager few take up most of the work. While Marshall's numbers - he claimed at most 25 percent of infantry fired their weapons at the enemy in combat - are very, very suspect, I haven't seen a similar debunking of Grossman's evaluation of air combat, so while I would say be cautious to accept his numbers uncritically, unless someone weighs in with sources showing to the contrary, I think they are roughly representative.
Would most missions have actually been uneventful?
I've recently been reading up on the 332nd Fighter Group aka the Tuskegee Airmen. When the 99th Pursuit Squadron first deployed to North Africa, they were flying missions for a month - beginning June 2nd 1943 - before a pilot scored the squadron's first kill on July 2nd. Although there had been a few encounters prior to that, some of the pilots had been flying as many as six sorties a day, and most of them never saw anything. All in all, it really depends on the mission. An escort mission into Germany is more likely to result in encountering enemy defenses, be they fighters, or at the least flak guns, than, say, a Combat Air Patrol over friendly territory, where it is dependent on being in the right place-right time when an enemy flight appears.
And so much matters on what country we are talking about, and when in the war also. The experience of the Tuskegee Airmen in North Africa is not going to be the same as, say, JG 52 on the Eastern Front, or Fighter Command during the Battle of Britain.
Someone else will have to weigh in on the other aspects of your question (and if someone would either support or debunk Grossman while we're at it, please do!)