To serve each work's creators [author; composer/lyricist] first and foremost, believing implicitly that they knew what they were doing and therefore deserve to have their work recreated with precision and complete attention to detail.
To serve the audience by "telling the story" clearly and with the highest levels of artistry, flair, and vividness. To remain cognizant of the fact that even the most popular works in any genre will have some people in the audience that are experiencing the work for the first time.
To always remember that the audience is the customer, and as such deserves to receive the best possible "bang for their buck." Artists' egos must never be of paramount concern.
To always remember that any semblance of "glory" or ego gratification can only come from serving the work. Any attempts to use material solely to demonstrate ones abilities is foolhardy and shallow. Talent must serve the work; to make the work serve talent will always result in flashy yet ultimately vacuous excess.
To remain cognizant that at every performance there are two important people in the audience: The one who is attending their very first live performance, and the one who is attending their very last. This constitutes an absolute honor and a solemn responsibility.
To always eschew vanity, egomania, or any grandiosity. As the great Michael Shurtleff said in his seminal book Audition, "Actors are not there to impress each other; they're there to impress the audience."
To avoid jadedness or any form of disdain for the art, realizing that working in the arts is a privilege and a joy –– and a gift, in that there are many people who would adore the chance to work in the arts. Furthermore, to avoid discouragement and/or jealousy by remembering that your disappointment at not getting a gig is the same feeling that others experience when you do get a gig.
And to always have the patience to explain what "gig" means. :-)