Two Tone-7
May I suggest that as a newcomer to Staff Travel you approach it with the attitude that you will get only what you are entitled to. Then if an upgrade comes up it is an unexpected but welcome bonus. The way the system works, it is out of your hands. As Juan Tugoh has pointed out BA has its priorities for staff just as it has for commercial passengers, and staff will be onloaded on that basis. I would call it bad advice to suggest that you will get something more than your entitlement by making a nuisance of yourself.
Unofficially of course friends of crew sometimes get upgraded after departure if space is available but I would not rely on that.
A Premium Standby ticket gives you a better but not guaranteed chance of a Club seat in that you have priority over those who have only purchased a basic standby ticket.