Hi Joel.Bravo to you for even raising the question. It has been my experience that a lot of folks THINK that they are called to music ministry. Eph 2 vs 10 assures us that God calls us, PREPARES us, and then provides good works for us to do.
I always audition people who want to join worship team. I have them play a few songs from charts, and then play a song of their choice. Prior to joining I have them fill out a questionaire/ministry profile. It gives me some insight into their background, skill level, temperment, and availability. I also meet with them AND their spouse, if they are married. If they are living out of wedlock with their significant other, have some obvious lifestyle issues, or are tempermentally unfit, we are done.
I like to meet with the musician and spouse because worship team requires commitment and participation. It does have an impact on the rest of the family. I find it really helps not just the person who wants to join the team, but also opens the door to discuss clearly what the expectations are, and just as important, what they are not. Many of the spouses are concerned about what is involved, time commitment, etc. I like to have everyone on the same page with regard to rehearsals, special music programs, etc.
I assume from your post that you have a handle on how to determine vocal range, ability level, reading skill, ability to follow lead sheets, etc. I use the audition process to get to know the person as well as access their musical skill. It is important to get to know "what makes them tick" so as to avoid learning "what makes them ticked" if you get my drift.
God Bless.