I was looking at long haul flights with BA. I have not flown long haul for some years now. I was shocked how much it is to select seats in advance, do you select them in advance or wait until online check in opens and run the risk of not getting window seat.
If you don’t want to pay, try and checkin exactly 24 hours beforehand and you will be able to change your seat to an empty seat free of charge. If the seat you want is not available, do not check the box to collect your boarding pass, and you can keep going back to check if more seats have opened up. Note that with basic economy, you will always have to pay to change your seat, even at online checkin.
Unlike Ryanair and Wizz, BA do not deliberately split up groups travelling together, meaning unless you are extremely unlucky, you will most likely be sat with your travelling companion.
Also one other thing worth noting is that BA allocate seats in the background 72 hours out, meaning that if you go to seat selection between 72 and 24 hours it may appear as if the plane is full up, however one of the seats marked as occupied could well be yours!