Bands are like marriages - for better AND for worse. No matter how well a band plays music, if things are rough offstage, failure beckons. Who can put on a good show after brawling in the back of the van on the way to the venue? Who wants to go through another tension filled rehearsal with everyone seething that you-know-who showed up three hours late again? For a nearly endless list of reasons, finding the right musicians for your band matters. Sure, musical prowess counts, but before you offer the keys to the empire to someone, here are some questions to help you decide if you're all on the same page.
If you're the type of musician that likes to rehearse on a regular schedule throughout the week and is very discipled about sticking to a strict practice routine, then you don't want to play music with someone who takes a very lax approach to rehearsals. The flipside is also true. If you practice kind of whenever, getting someone to join the band who prefers a regimented approach towards rehearsals is going to drive you both batty. Have an open discussion about the importance of availability for rehearsals and who you both see your responsibilities in this department - not only will this help you see if you're on the same page in terms of practicing specifically, but also if you're approaching your music careers with the same degree of enthusiasm.
Not all musicians want music to be their full time jobs. Some players want a band they can gig with on the weekends around their other career and are content to stay in that position. Others, of course, want music to the occupation. Which are you - and which is your potential band mate? If you're at odds over this one, your band is destined to fall apart. If you want to go full time with your music and your band mate can't realistically get off work to tour, for instance, you've got a problem on your hands. Music has to be the same kind of priority for you both, or you'll be working at odds with each other.
This one cuts in both directions. If your music is essentially a hobby or a side job, and someone working hard to pay the bills with music commits to your band, then they're going to get frustrated that you're not being active enough to let them progress and earn an income. Don't try to tie someone down to your project if it's going to hold them back from their goals, no matter how awesome they play.
If your band collaborates on writing songs, then adding a new member who is ready to chip into the process can be exciting. If, on the other hand, your band has one chief songwriter who is used to creative autonomy, then adding a new writer to the mix can be a recipe for confrontation, especially if your new band member expects the band to entertain playing their songs. You can really only take this one on a case by case basis. If you're existing songwriter is cool with sharing the responsibility and letting someone else's work get some shine, then no problem. If your existing songwriter prefers to keep things status quo and the new guy/girl is cool with not adding their songs into the mix, that's also fine. However, if your new band mate is a serious songwriter and your project doesn't give them an outlet for that, then don't be surprised when they start turning their loyalties to a new music project that beckons that DOES let them air their material. Best to have these discussions up front than to wait for them to become an issue.
Bands have financial concerns. Depending on where you are in your career, this can range from everyone throwing in for some practice space and some beers to everyone splitting the profits from a national tour. It's important for everyone to understand how these things will work, particularly before any money actually starts coming in. If you expect a new band member to contribute to your expenses, say so up front. If you expect to split all income equally between band members, say so up front. Bands crumble over these issues, especially when they're on the cusp of making real money for the first time, if they haven't worked these things out in advance. Make sure your potential band member knows where you stand with these issues and that they're ready to get on board with the way things work.