After about two decades of leading music in a dozen or more churches, both Catholic and Protestant, I've taken a long break and am focussing on just getting my growing family to Mass on a weekly basis. These notes and recommendations come from my experience leading music, and comments from others. Feel free to write if you have additional comments that you think would be helpful.
These are intended as helpful tips and pointers -- not as criticisms of any individual. Persons wishing to improve their liturgical music programs are encouraged to consider these points and to gradually adopt them, one or two at a time, over a period of several months (or even years).
Musicians: This is a lot of information and too much to try to attempt all at once. If someone has left this for you, they care about you, the Mass and the parish. Try not to take it "personally."
Liturgical music isn't about you, your skill, or about just showing up and playing some tunes. Implementing a good liturgical music plan can take a long time. Positive results (in the sense of prayerful, singing parishioners or positive comments) may take months or even a year. And some people will always complain loudly about any change, good or bad.
Learn to tune your instrument, and do it well before Mass. This is especially critical for guitarists, or any instrument when played with others. Many amateur players can't hear when their own instrument (or voice) is out of tune. Really.
Many groups treat liturgical music like a pick-up basketball game. However, you really should have semi-professional talent before you seriously consider leading liturgical music. This is not "amateur hour." In the absence of such skill, a clear voice and can count for a lot, but much more practice is necessary.
Do not play or practice in the church during the ten minutes immediately prior to Mass. Parishioners often use that time to pray and prepare.
Along with developing musical talent, the best possible thing you can do is learn the Church's perspective regarding liturgy, the Mass and music. Insofar as you can, study and understand the structure of the Mass, the meaning and history of the different elements and the directions and intentions of the Church regarding participation. The starting point for this is to personally read the fundamental documents about the reform of the liturgy, especially Sacrosanctum Concilium. Don't rely on anyone else to do this. This should be required reading for the group leader, if not all participants. Most people who talk about Vatican II – especially liturgists and musicians – don't actually know a thing about it and have never read a single document from the council, itself. You can usually disregard advice from anyone who uses phrases like “spirit of Vatican II.” I assure you that they don't have any clue what the council actually instructed, but are just using the catch-phrase to cloak their own desires.
Your “success” as a music leader or assistant depends on your ability to harmonize your musical talent, personal faith and understanding of the liturgy of the Mass. Insofar as any of these areas are weak, the liturgical music will struggle (or can become a dysfunctional attempt to make up for a weakness).
Do not change musical selections too frequently. You will be bored with the music well before the congregation has even begun to learn it. In fact, the majority of the music you select for any particular Mass should already be known and liked by the particular congregation. That song that you've played a hundred times, and are now tired of? The congregation heard it for the first time last week... just two verses. It will take them several more exposures to it to learn it. In other words, you shouldn't introduce more than one or two new songs per month.
When leading liturgical music, you have to be simultaneously prayerful and professional. Both must be present, but they must be balanced; one dynamic cannot be allowed to override the other. If you are “too prayerful,” the music may be too slow and without rhythm. Don't get caught up in the music such that you lose track of its purpose, which is to help the people pray. If you are too professional, then the music become stiff, perfunctory and cold. It is like a chore or a march that one has to get through so he can move on to other things.
Your group should practice together weekly. Those who do not practice should not be in the music group. The amount of practice necessary is proportional to the number of people and different instruments present in the music group.
Select music that helps people pray, not necessarily music that you like. There is a vast difference between music that is appropriate for personal prayer time or that makes for fun playing/singing and that which is appropriate for Sacred Liturgy.
Solos are generally a bad idea in liturgical settings.
It is not a performance. The music should draw attention to Christ, not to you, and culminate in reception of the Eucharist. Talented musicians in particular need to moderate their playing and singing so that they are at the service of the Mass, not its focal point. Frequent applause for your “performance” is generally a bad sign. If all is well, people will leave thinking “what a great Mass,” not “what great musicians!” This is especially difficult for skilled musicians who tend to derive a lot of personal value from the attention prompted by their performances.
Any participant in the music leadership should be a practicing Catholic with a public life in keeping with the Church's teachings, and should have exceptional musical skill.
The Gloria should not be longer than the homily.
Keep it simple, especially for the Responsoral Psalms. The chant lines provided in most parish books are too complicated for most parishioners. Simple chant tones are often better.
People don't respond well to large and rapid changes, especially to the Liturgy. Any changes you make to the general liturgical music program should be very carefully thought out, have as their goal an increase in the prayerful participation of the congregation, and be made very gradually -- over weeks or months. For example, if your parish presently has very little music and the Mass is generally recited, you might add opening and closing hymns... then wait two months. Then spend two months learning a simple chant for the responsoral psalm. Then another two learning an arrangement for the Sanctus and Agnus Dei. And so on. Just don't try to change everything at once, or people will be rightly distracted and frustrated.
Include an annual (or more frequent) questionnaire in the bulletin asking for feedback, song and other suggestions. Pay attention to it.
You probably don't sound as good as you think you do. Record and listen the liturgies at which you assist. Then do what you can to improve.
Do not stand up immediately prior to (or during) the Great Amen. Either do so well before it (and only if absolutely necessary), or wait until after. Otherwise, parishioners are confused by your movement.
Improvisation is for jazz, not for liturgy.
When announcing a song, do so clearly, loudly and repeat the number. Then allow the congregation time to get the books, open them, find the page, etc., before beginning the first line.
Do not make distracting movements during the liturgy. Your general approach should be to support and blend, not draw any attention to yourself.
Insofar as possible, you should not be singing at, to or for the people, but with and in support of them.
Never, ever select songs that are in a foreign language unless that language is native or known to a majority of the congregation. Many musicians make this mistake, thinking themselves “inclusive,” when all they are doing (if they were to pay attention) is annoying the congregation and silencing everyone.
Avoid “Bowdlerized” music. This is music that has been substantially altered from its original for reasons of political correctness. Such music almost always is less poetic and usually perpetuates some very bad theology. You can recognize it almost immediately by awkward phrasing and strangely-frequent use of the notoriously unmusical word “God,” which was used to replace instances of “Him,” “His,” etc.
If you are leading a song, and you glance out and notice that most people have their mouths clamped shut or are mumbling inaudibly, you are doing something wrong.
Watch your tempo. Many amateur musicians play tunes either much too fast (being nervous), or way too slow (trying to be prayerful) for a congregation.
Avoid overly-difficult songs unless they are already familiar to the congregation. Many modern liturgical songs seem to be written for professional choruses or stage plays rather than common churchgoers.
If you lead music at a Mass, consider attending a different Mass for your own prayer time.
Quality musicians who spend time and talent practicing and leading music should receive a modest stipend for their efforts, just as a visiting priest often receives a stipend for celebrating the Mass.
Coordinate music with the celebrant not right before Mass, but days in advance. There should be a liturgical plan for each Mass that lists each reading, song, etc. a week or more in advance.
Avoid common, canned music and liturgical planning services. The selections, prayers and the like usually leave much to be desired, and rotate music too frequently.
Learn chant. Chant -- Gregorian Chant in particular -- is a fundamental part of the Church's musical heritage and should be used in the Mass when appropriate.
Never criticize the congregation or command them to sing. If they aren't singing, then you are doing something wrong.
Be open to criticism and willing to change (or quit) if what you are doing isn't working. It may be that your talents are not beneficial to a particular parish at a certain time.
Musicians have a (bad) habit of trying to fill every moment with sound. Sometimes no music is the best choice of all.
I've yet to see someone who is skilled enough at guitar that they can properly play a 12-string, keep it in tune, sing and lead liturgical music all at the same time. It is almost always out of tune, played like an autoharp, or otherwise poorly played. If you don't have semi-professional guitar skills, stick to a 6-string.
Be light-handed with electronic instruments and effects. If you can distinctly hear the effect, then it is probably being over-played, will be a distraction to the congregation, and should be cut back.
If you assist at multiple liturgies, consider having different levels/kinds of music in each, and be consistent. For example, more traditional music at the vigil Mass, little music or just chant early Sunday morning, or more contemporary music at the 10:00 AM Sunday Mass. It depends on the attendance patterns and tastes of the congregation.
Avoid music that is about "us," "our stories," etc. The proper focus of music during the Mass is on God, worship and prayer.
You and other assistants (and the music as a whole) will benefit from you having a proper, informed understanding of lay ministry and the lay apostolate. Assisting in the parish, whether that is in music, greeting, or any number of other ways, is a good practice. But it is not the calling of the laity, nor is it the normal path by which laity grow in holiness. Liturgical music is particular a way by which you can assist in the liturgy, but your “ministry” and that of the laity in general, is in service to your family and neighbors; this takes place primarily in the world, not within the four walls of the parish.