Don't forget Online Check In (OLCI)
As you're a BA Exec Club member you should be able to check in for your flight 24hrs before your flight leaves. As only 30% of seats are up for preallocation, you should be able to snag yourself a better seat through OLCI. If you don't manage to get a better seat, you still have your old preallocation to fall back on.
Non-members of the Exec Club who are registered on the website can use OLCI at T-12hrs.