It might be cold sitting in the audience, but it's very hot in the Hot Seat, with the combination of the studio lights and nerves.
I haven't been to the Studios yet (or WDW at all - under 50 days, woohoo), but I was lucky enough to get into the Hot Seat at California Adventure last year. Somehow, I actually made it into the Hot Seat on my first try, so I must have been doing something right. I assume the game is played virtually the same way in Florida, so I'll offer my thoughts. This is long, but thorough...
As was mentioned, the fastest finger is pure luck. There are only 24 possible combinations, so in an audience of 600 people, the chances are 25 people will get the right answer simply by button-mashing. In the time it takes to think through the right answer, a bunch of random guessers are already locked in ahead of you. Pick your combination and mash away. If you don't pick the right combination, don't fret, the fastest finger rankings are not included in the regular game. Also, have every member of your family mash a different combination to increase your chances. Young children who mash their way into the Hot Seat are allowed to have a parent join them to "help out", so you could get into the Hot Seat by proxy.
When you're playing along in the audience, the most important thing is to know the answers. I know that sounds obvious, but if you don't know the answer right away, before any of the choices are given, you're chances of getting into the Hot Seat are greatly diminished. The most important thing is to be able to answer the question once it is asked, that way you're only waiting for the correct answer to be revealed.
For example, if the question is "What color is the sky?", all you have to do is wait for "Blue" to show up in the answer list. If you have to wait until all the answers are shown before you answer because you're not sure, you'll be beaten.
Next, don't look at the keypad and don't wait for the keypad to light up. The keypad becomes active once choice "D" is revealed. If you wait until you "see" the keypad light up, a bunch of other people have already locked in their answers. Once the correct answer shows up on the screen, begin rapidly and repeatedly hitting that button. If A, B, and C are not the correct answer, begin hitting "D" the instant "C" pops up because "D" must be correct. This is where knowing the right answer becomes critical.
I use a technique honed through years of winning free drinks and bar tabs playing NTN in the bar. I use my middle and index fingers on each hand and put one on each button (i.e. left middle finger on A, left index on B, right index on C, and right middle on D). As each letter is revealed - if it is wrong, I lift that finger off the key - if it is right, I start pushing it. Push the button by rapidly and repeated tapping it as fast as you can. You want your answer to register as soon as electronically possible (not as soon as humanly possible). If you have to look at the keypad, you'll be too slow.
Don't overthink the lower point questions, they're supposed to be easy. If you think "A" is right, it probably is. At the very least, commit to an answer by the time "C" comes up, if you're wrong, there's always the next game. If you wait until "D" comes up before making a choice, you'll be too slow to get into the Hot Seat anyway and there's no difference between #2 and #200 at that point.
Work with the other people in your party to increase your chances. I would classify the questions like this: 1-5 are basic general knowledge, which the majority of people should know before any choices are revealed (they tend to skew towards American topics, so questions about baseball are more likely than questions about cricket). Questions 6-10 are what I would call specific general knowledge. If you have a basic knowledge of the general topic the question is about, you should be able to answer it (the question that got me into the Hot Seat when the first guy got it wrong was about Pokemon. I know approximately four things about Pokemon, luckily the question was about one of those 4 things). As the point values increase, the questions do become more difficult and require a more specific field of knowledge about the topic (my 32,000 point question asked "Which of these Zodiac signs is considered a 'fire' sign?" - Luckily, the correct answer was Leo, which is my sign). The final 5 questions, 11-15 are the killers because they require a very specific level of knowledge about a topic and each question covers a topic very different from the last. You might struggle with the 64,000 question but know the 250,000 without a problem just because they are different fields of knowledge. The challenge is to able to 'run the gauntlet' of the final five to win the Million. By working as a team, your group increases its chances because you're collectively going to have a broader base of knowledge than you do individually. Some questions even skew towards children's knowledge, so don't be afraid to consult with your kids (just do it quietly, so everyone - especially the person in the Hot Seat - can't hear you). Even simply watching what the other person is entering and copying would work well. If you finish #1 & #2 by working together, it's better than being #5 & #25 by working alone.
Once you get into the Hot Seat, soak it all in and have fun. After all, until you get to the Million point question all you're playing for is pins and clothing (albeit very cool clothing). Don't overthink the easy questions, but do think about them. You have a time limit to answer, as long as you say "Final Answer" before it hits zero, you're okay.
Something I learned in hindsight...if the "exact" answer that you "know" doesn't show up, don't automatically go with the "closest" answer. Look at them and think it through. In the higher levels, sometimes the "obvious" answer isn't correct. For example, the question I lost on (the 250,000 level one) was "In a newspaper what does 'Op-ed' stand for?". My first instict was "Opinions and Editorials" (which is a correct answer), unfortunately, that wasn't one of the choices. However, "Opinions of the Editors" was a choice, and it was the one I chose before thinking it through. If I had thought about it, I would have realized that Op-ed pieces are written by people who aren't on the editorial staff (otherwise, they would be Editorials) and often present opinions that are contrary to the Editorials. The correct answer was "Opposite the Editorial" because the Op-ed section typically appears on the page facing the editorial. At that point, after using all my lifelines on the previous two questions, I was so happy to have a question I "knew", that I didn't think about it hard enough.
For the lifelines:
I'd save the Ask the Audience for the final one. Remember that they use the answers the audience gave when the question was first asked. These are the answers that the people are trying to win their way into the Hot Seat with, so they aren't going to try to fake you out. The odds are that even a small percentage of the audience is going to know the answer to each question, and the people who are guessing will cancel each other out, therefore, the ones who know will make up the difference to put one answer in the lead (in theory at least, this becomes less likely as the questions get harder and the guessing and "educated guessing" increases).
50/50 is a bad one because it usually doesn't help. Typically, you can eliminate one or two of the choices by yourself. When you use 50/50, you probably won't be much better off. I believe the game is programmed to eliminate two specific answers and doesn't do it randomly. I was asked about test pilots in the 1920's and two of the answers were Chuck Yeager and Buzz Aldren. I knew Aldren went to the moon and Yeager broke the sound barrier after WWII, but I knew nothing about the other two choices. I foolishly used the 50/50 and it took away Aldren and Yeager, so I wasted the lifeline and had to ask the audience to stay alive. I should have saved the 50/50 for the next question about the voices of Mickey Mouse, where I was only able to eliminate one wrong answer on my own.
Phone a Complete Stranger is a crap shoot because you have no idea who's on the other end of the phone or what they know about. I used this on the Mickey Mouse question and luckily someone recognized one of the choices as the voice of Donald Duck, so I chose him and was right. Also, something I did that people don't seem to do is not read all of the choices over the phone. If you know that one of the answers is wrong, don't waste time for risk confusion by giving it as a choice. In my example, I knew that Walt Disney was Mickey's original voice, so I didn't say it as one of the choices (which was funny because I heard a woman behind me gasp as I skipped over Walt's name). The host pointed out that I had missed a name, and I said "I don't have to say it, do I? I know it's wrong." She sort of shrugged and said "I guess you don't have to say it." I remember seeing this happen on the tv show where the contestant was able to eliminate an answer in his own mind, but his "Friend" got hung up on the wrong answer and ran out time before answering the question. As a result, the contestant got it wrong and lost. I vowed to not make that mistake if I ever found myself in the Hot Seat (never expecting that I would, since it was before California Adventure was even built).
That's all I can think of right now, and I've been waiting almost a year for someone to ask me.