Know lots about the company, from stock price to future plans or programs.
If you can, learn something about the person(s) interviewing you. Background, time with company, etc.
If the do international work, know something about international ops, easily researchable.
Do NOT throw airline type questions--seniority, bidding, upgrade time--have no place here. Understand a bit about how they fly, where, do they have a flight planning provider, what kinds of flying they do--business, some personal flying for the CEO, that sort of thing.
Ask about what additional tasks you might be assigned--safety, charts, training.
GF