BA's recruiting literature gives almost all the clues you need about the kind of people they are looking for. BA are no longer the automatic choice of airline for UK pilots, so they are having to work somewhat harder to persuade people to join them than they used to. Nevertheless, as with any propsective employer, you should familiarise yourself with their business, their future plans, their recent results, and the market context for these facts. You should also have a good think about how you, as a pilot, could help the company to bring about its business aims.
Lastly, there are some extremely good threads on this forum about BA recruiting and interviews. Go back a few years in your search; you'll find not much has changed.
Scroggs