Prefer to sit together
My wife and I prefer to sit together, and have almost always been succesful after upgrades or irrops. Some of my thoughts regarding the below -
1) We usually try to board early, and know specifically what swap will be required (Window for aisle, forward or back, etc) so we can ask the passenger as they approach their seat if they would like to switch, and the reason (So my wife and I can sit together). We ask once, and take a no for a no, without prying. Once their bag is in the overhead, it becomes more difficult for them to switch.
1a) Getting someone to swap an aisle for a window is more difficult, as is a middle for anything else in coach.
2) In FC, if FEBO will result in a poorer meal choice, I will always ask the FA to offer the choice to the passenger who swapped. And if they have moved a row back, I will allow them to exit the plane before my wife and I.
3) In a coach IROPS situation, I will offer to buy a drink or sandwich for the person.
Usually works, not always. Some luck with GA, but generallly ask them if there are available seats to swap to, and if no, will not ask them to try. If they voulenteer, We'll let them.