So how do you do it? I’ve been flying now for well over 10 years, but I haven’t once been bumped to first class! Yet I know friends who have had it happen to them multiple times!
What’s the secret? Do you have to go up and ask? Get put on some kind of special reserve list?
I mean, seriously, with the number of flights I’ve taken it would seem like the odds would be on my side…
It normally depends on two things. How many frequent flyer points do you have, and what sort of ticket do you have? That’s about it.
It just happens. It helps if you have elite status with their frequent flier mileage program, but I’ve been bumped a number of times.
For me, the “secret sauce” was to be in the carrier’s frequent flyer program, and to be paying pretty close to full fare for unrestricted business class seats. (Usually, my fare code was a plain ol’ “B”) My employer’s own travel service set me up in the fairly expensive seats - I certainly wouldn’t have paid those fares on my own, but for as many hundreds of thousands of miles our people were flying per month, we probably got a pretty good deal.
After five round trips and a handful of mileage bonuses for things like signing up for the program, using online check-in, etc., I had enough for an upgrade. As luck had it, it was my last flight with them as that particular project that had me jetting cross-country each month was finished.
I’ve been bumped from Economy to Business class twice on international trips.
The first time was back in 1996, on a flight from Vancouver to Sydney via Honolulu. It was late January, the plane was half empty, and i was one of the first people to check in.
The second time was on a flight from Dulles to Heathrow. My plane was due to leave at about 9 p.m., but had been oversold so they asked for volunteers to take the next plane, leaving two hours later. I had arranged to meet a friend at Heathrow about three hours after my flight landed the following morning (she was flying in from somewhere else) and was going to have to hang around anyway, so it made no difference to me whether i sat waiting at Dulles or at Heathrow.
I went up to volunteer for the bump, and the woman at the desk was very thankful. Then, a few minutes later, she told me that they may not need me to switch after all. I said no problem; i didn’t care which plane i was on. Then a bit later, she said that they didn’t need me to switch, but because i had volunteered she had put me in Business class. Sweet.
For a while a few years back, i had been flying United frequently enough that i was placed in their Premier club, or something. The membership lasted for a year, i think. I flew three times that year, and each time i got upgraded to their Economy Plus seats, with more legroom. Not quite Business or First Class, but a nice bit of extra room.
ETA:
To add to what the others have said, i think nowdays if you’re not a premium or elite frequent flier, and if you buy your tickets on discount sites like Expedia or Travelocity, your chances of getting upgraded are virtually zero.
I saw two active military get upgraded to First Class when they checked in at the gate wearing their BDUs (Battle Dress Uniforms). Made me all warm and fuzzy on the inside.
I’ve been bumped to first class twice: once from Sydney to New York and once from Rome to Sydney. It was a few years ago, when I was doing a lot of international travel for work and was accumulating a large number of frequent flyer points. In both cases I already had a business class ticket. In the first case I asked at check-in. In the second case it was just offered to me, largely, I think, because the first class cabin was practically empty.
I have been bumped twice from Europe to the US from Economy to Business (no First on Delta trans-Atlantic). I have quite a few FF miles with them and have a “status” level too. I was using them frequently last year as they provide Prague-Atlanta service which I used at least half a dozen times.
Sadly, on Emirates (my favorite carrier) I have never been bumped up despite a bunch of flights.
Only been bumped up once, from economy to business class on a Bangkok to Hong Kong flight. The wife and I both. Economy was overbooked, so someone had to be bumped up. They chose us. Dunno why.
Fly on a staff ticket and be related to someone high up in the airline. That’s how I always get into first class & the lounge. 
Other things that help are: being dressed smartly and acting professional. You can try sweet talking the counter staff but they’ll probably laugh at you. Fly on busy, almost fully booked flights so they have a reason to move someone. You’ll only get into first if you’re paying for business and they’re over booked. If you are at the counter when they run out of business seats, look the part, you’ll be the one upgraded.
Any attempts at hissy fitting your way into an upgrade will probably get you bumped off the flight.
No way will you be bumped from economy (coach?) to first. Business, business-look and frequent flyer miles are the way. They want to give the perks to the people who give them the most money.
I’ve been bumped twice, once on Virgin from Premium Economy to First on a flight from London to LA, and another on BA from economy to business on a flight from Orlando to London. Both times it was full-fare ticket but no frequent flyer miles.
Got bumped last September, flying from Miami to Cozumel on American: Economy to Business. We’re not frequent fliers, we don’t belong to a travel program, and we purchased through Orbitz. We weren’t the first to book our seats, nor the last. We weren’t late to arrive, nor early. The flight seemed full but not overbooked. As they were swiping our boarding cards to get on the plane, it was announced that we had been moved to Business Class. A delightful surprise, but a random one, it seems.
It has only happened to me once. In that case I was flying to Japan, we had booked our flights many months in advance and we were regular customers. The plane was too crowded so they bumped me to first class from business class and bumped someone from coach to business.
I get bumped up about 50% of the time on domestic flights. Hasn’t happened yet on an international flight, but there’s always hope.
When you check in on line at the carriers site it automatically puts you in the que for upgrades.
I personally have been bumped up only twice (once on CO Houston/LAX, and once KLM Amsterdam/Johannesburg, that was sweet). Both times were coach to business, but I don’t really go after it and my bumps were pretty much random. OTOH, one of my bosses (a well-dressed Brit who has a rep for being able to sweet-talk the birds down out of the trees) has a go at getting bumped up every time he flies, and claims to be successful close to half the time. As others have said, it seems to help if one a) looks the part, and b) has a lot of frequent flyer miles and/or a full-fare ticket.
That isn’t always the case. I have been bumped from coach to first class a few times. The circumstances were usually unusual though. Volunteering to get bumped is a good way as is being on standby because of an airline mistake. You need to be dressed well and be reasonably attractive. They aren’t going to bump a 300 pound mouth breather in sweat pants to first class no matter what. Minimum dress requirements to get bumped to first class would be something like chinos and a polo shirt for a male and a nice dress or business attire for a female.
Well, that explains why I have never been bumped up. When I travel by air, I am all about comfort. 
I was bumped up at a restaurant, though. Last weekend I was out with my gf, and we stopped at Mitchell’s Fish Market for dinner. We ordered a mid-priced bottle of wine. The manager came over and apologized that the last bottle had been sold. He pointed out a “suggested alternative” that was 3x the price, charging us for the cheaper bottle. 
My most recent bumps were because I have a lot of frequent flier miles with United. So I’ve twice been upgraded from Economy to Business while flying between Sydney and San Francisco – and thhis is really sweet, because it’s a 13-hour flight, and the different in comfort is considerable.
About 12 years ago I was bumped from Economy to First while flying from Hong Kong to Beijing on Air China. Since that was my first flight on that airline, I suspect I was bumped because I was Caucasian – when I went to join the queue to check in at Hong Kong, an airline employee spotted me in the line of Chinese people, and sent me off to the first-class queue. (However, I stayed in Economy on the return flight).
Of course anything can happen in unusual circumstances, but if one is looking to get an upgrade everytime one flies it’s worth noting they’re being unrealistic to expect an economy to first upgrade.
I completely agree re: dress code requirements, being attractive and flying standby (for any reason, not just the airline’s mistake).
Additionally, it occurs to me that it might be easier to get upgraded on a shorthaul flight. I generally fly 7hr+ international flights, so I’m not familiar with how operations run on shorter domestic/international flights. Most short haul flights I’ve taken in Europe have been fully booked and only consisted of economy & business, so there was not much room to seek an upgrade.
One final unsual circumstance that might help is being on an extremely empty flight. A few times I have been on a flight that had only two or three business class passengers and three or four first class. We were all seated in first class so that the crew could close down the business section, making less work for themselves.
I have also had occassion to be the only person flying in first class and the attention can be overwhelming and oppressive - they had up to four people just waiting on me and it was rather uncomfortable. They were very polite and professional but also extremely eager to please. I almost wished I had asked to be downgraded, but everytime it happened I only noticed I was alone when we were in the air. I do not know if they will downgrade you at request.
I was bumped up once when my late evening plane was grounded with a bad tire and they gave me a choice of another flight in the wee hours but first class, or a hotel room. I chose the former but was so tired I couldn’t tell the difference as I was asleep before takeoff.