Coming from a traveling family, I was confirmed in the Church later than most, when I was 16. It was at this time that I led my first song at Mass: Gift of Finest Wheat, which was NEW then! The church musicians told me they could not play it so I led it a cappella.
Good melodies do not require any instrumentation. As I said in a previous post, if a melody requires the harmony to sound good, I avoid using that hymn. However, a good accompaniment can lend beauty, energy and excitement. And if you have a congregation that is still finding its voice, you can use instrumentation to lead them and allow them to hear the beauty of their singing without covering it up. So here are a few pointers for accompanying a needs-to-sing-more congregation:
1) When using a percussive instrument, like a piano, recruit a sustained instrument to double the melody. Having that melody presented strongly makes the congregation feel more secure. If you don't have a sustained instrument, you'll most likely need to sing along, but keep the volume such that they can clearly hear themselves sing. Try for a balance so that they can hear you about as much as they can hear themselves.
2) When using a sustained instrument like an organ, be careful of what stop settings you choose.
For starters, leave the celeste stops for instrumental pieces. If you want a congregation to sing on pitch, the pitch needs to be obvious, not blurred.
I also avoid combining flutes with principles. I realize I'm in the minority here, but go to the organ and experiment. When you combine a flute with a principle, in general it creates a more "woody" or blurred sound. It's beautiful, but I don't feel it provides the base needed to support hesitant singers. I've had other organists tell me that they must do this for volume, but often there are work arounds with creative use of couplers. For example, pull a string from the swell to the great using both the 4' and 8' couplers.
So I stick to either flutes by themselves, principles alone, flutes and strings, or strings and principles when leading congregational singing. And I pull different octaves from the choir and swell to make it possible to have variety while still sticking to easy to follow solid tones.
3) When your singers are unsure of the melody, play it in octaves and leave the rest out. It can be very effective to play even the first part of a hymn line, and then finish the line with a cadence. For example:
Melody Chord Chord Chord
Immortal, invisible, God on- ly wise
4) As an organist, you need to listen and adapt. While I'm all for pre-sets, and do love to come up with fun registrations, I find I have to be adaptable. When a congregation is singing strongly, I can add a trumpet descant to a final verse. If they are barely singing, I switch to emphasizing the melody. How loud the organ is varies according to how many people are in the church, how many are wearing coats, and how loud they sing. If I play too quietly, they don't feel supported. If I play too loudly, they cannot hear themselves sing.
I hope these few ideas inspire you to come up with your own list and share it in the comments!