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Know your company fuel policy inside out, upside down and every which way. (Know when to continue to destination, when to leave/stay in the hold, when to divert, minimum fuel requirements should be as familiar as your home phone number.) Be able to check the load sheet (manual and also computer generated) and the the tech log with your eyes closed (metaphorically speaking). Know how to work out the flight time limitations from the impossible graphs and tables that your company will provide and get it right every time. Know the difference between company and regulatory FTL.
Act like a captain from day one, but never forget what it's ilke to be the F/O. Remember in twenty years time you'll still be learning the job. The buck stops with you-discuss and delegate when necessary-but remember it's your decision making process in the end.
Knock 'em dead. It's the best job inthe world.