I’ve seen various questions on TSE about ruses to ‘’sneak’ into a higher grade cabin than the one paid for. I’m interested to know what the chances are of being upgraded legitimately (i.e. by the airline) on a long haul flight and what, if anything, a relatively infrequent non-business traveller can do to improve their chance. In all my years of flying on vacations, I’ve only ever been upgraded once with BA, and that happened simply by asking politely at checkin.
In these days of yield management and frequent flyer programs as a profit center, getting upgraded without any status is increasingly unlikely. But if you want to improve your chances...
The likeliest way to get into business without paying for it is to volunteer to be bumped. This obviously requires that a flight is so overbooked that the airline needs volunteers to fly later, and is desperate enough to offer business class to people willing to fly on a later flight. To make this happen, ask if the flight is looking full when checking in and offer to help out if needed. (If you wait until they start looking for volunteers at the gate, somebody else may beat you to it!).
A riskier option is to check in at the last possible minute. If you're lucky and economy is all full, you just might get a bump to business. However, these days it's more likely that somebody with higher status than you will get the bump up instead.
Last and least, you can simply ask. I once asked how much a trans-Pacific upgrade would cost, and the rather new/clueless looking agent spent a good 5 min poking around before saying it would be US$5000. I declined... and was rather surprised to have my boarding pass go "ding" at the gate because I had been upgraded! (And no, I wasn't charged...)