Be mentally present, be a co-thinker not just a co-follower.
What I mean by that is anticipate decisions.
How much fuel would you take today and why.
CB’s on your route, deviate left or right and why?
Choice of runways at your destination, which one would you request and why?
As a CA I ask those questions to my crew members. If they give me an empty stare I know they haven’t even considered the choice.
You can question my decisions every day all day, just be a little diplomatic about it.
Starting every question with WHY?! is annoying.
Over time you’ll experience that your ‘mental’ decision matches your CA’s actual decision.
If not, ask.
Why are we taking the short runway when it’s raining?