Points to consider (here are some things I think about, when we do
auditions):
We hold them, even though we might not have an immediate need for more
musicians. It gives us backups and lets people know we want their
participation and value their contributions in any talents they may have.
You have to decide the level of musicality you are willing to accept.
My suggestion would be that you get 2 musical people (possibly from
another church, if you don't have them in yours) to help you do the audition.
One person should be a vocalist who can help evaluate singers, and another
should be an instrumentalist who can evaluate more than one instrument.
Complete the entire auditions (one person at a time), and make a written
evaluation of each. Between yourself, and your two musical friends,
you should have 3 evaluation sheets on each person.
Do NOT give the results or say yes or no at the auditions.
Instead, meet later with the 3 of you and discuss each person and your
respective results. Do this intelligently (using your natural senses)
and spiritually (prayerfully asking God what he wants for your team).
I use musical, spiritual, and team unity issues to determine whether
or not to add a specific person to the worship team. If they have the musical
ability to help your worship, that is the first step. Sometimes I
will get a strong sense of God's presence when people worship, and you
can sometimes see a clear desire to worship (not just perform) through
people's mannerisms. One of the most important things for me is how
well the person fits in to a group of people. Are they abrasive or
argumentative? Do they project their personality in order to be noticed?
Are they willing to just "play a part" and not be a "star"?
Answering some of these questions honestly will help you determine whether
or not the person will make it in a "team" environment.