By Matt Putnam

Things you are responsible for

Evaluating auditionees’ vocal abilities at auditions/callbacks
Leading all vocal rehearsals
Coordinating with the Orchestra Director regarding musical logistical issues (entrances that are hard to find, cues, etc.)
Ensuring that technical and stylistic decisions between cast and orchestra are consistent
Leading vocal warm-ups during prod week and before performances

Schedule

Look through all of the music and determine all of the vocal requirements for all of the characters. Obviously this includes the ranges of the parts, but it also includes the quality of the voice and any particular abilities needed to properly play the character.
For all characters, determine what deficiencies in vocal ability would make an auditionee uncastable for that part. The range is a starting place, but also consider tuning, sense of rhythm, ability to harmonize, vocal strength, and breaks. This includes not only the named characters, but the ensemble as well. You will need to make a case to the CRB in order to help define who can be cast, so be thorough.
Pick the vocal selections that you want to hear for callbacks. You need to have this done a few days before auditions so you can handle early auditioners and anyone else who can’t make the regularly scheduled callbacks.

Determine what you want to hear from the auditionees and make a plan for auditions in conjunction with the rest of the dir staff. Typically, we ask auditionees to sing a short excerpt (“30-45 seconds” or “16-32 bars” are common phrases) and do a range check for the vocal portion. For vocal-heavy shows, you might want to ask for two contrasting excerpts, but be aware that many auditionees will still bring just one.
In the audition, don’t be afraid to cut someone off if their excerpt is going long. Commonly, people will know the whole song and will just keep going until someone stops them. Also don’t be afraid to stop them and ask them to start again if the accompanist (or the singer... but blame it on the accompanist) messes up badly enough to throw them off. If you and the other dir staff members manage to create a casual, friendly atmosphere, this shouldn’t freak out the auditionee.

Discuss the style and direction of the show with the director, and make sure that your vocal plans are in line with the director’s vision. Also check-in with who will be on stage at what points (especially for ensemble members who may be playing multiple characters) so there’s no confusion there.
Go through all group numbers and decide how to split parts. If ensemble members are being split in different ways throughout the show such that the voice type distribution changes significantly, it’s okay to assign people different vocal parts for different songs.

Do your homework. Go through the song you’re rehearsing and learn how each part goes. You’re supposed to be the authority on the music.
Double-check with the director about who’s on stage. It’s a bad situation to have to re-split parts after they’ve been taught because you realize that all of your altos are off stage changing their costumes at one point.
Be aware that cast members have wildly varying levels of experience and musical skills. Some people will come in reading music extremely well, knowing all of their intervals, knowing theory, etc., and others will not be able to read music at all. Have a plan for how to accommodate all of these people.
Remember to plan for an accompanist, if you need one.
Don’t forget about warm-ups!

Encourage everyone to take care of their voices. Force feed people water, tea, honey, vitamins, or whatever you prefer. Prod week plus the first weekend of performances is a solid week (or more) of strenuous vocal work.
If there are ever offstage singers, get the sound engineer a thorough and up-to-date list of exactly who is singing offstage and when. If plans change (e.g., an actor who was once singing offstage now has to do a costume change instead), make sure that gets communicated. Otherwise you’re going to get, “augh, my zipper’s stuck!” blasted into the audience.
Unless there’s still music to teach, or something needs review, your job is pretty much over. You will be leading vocal warm-ups and doing any emergency rehearsals, but the more you can eliminate stress by letting things go, the happier everyone will be. Pick your battles wisely.