I think many of the best hymns almost "sing themselves" - they have intervals between notes that are not too unusual, and the tempos are usually pretty standard. In a typical church anthem, the first, second, and fourth lines are the same; and the third line is a variation related to the other three - so, basically, you learn the tune of a hymn by learning just one line.
We Catholics have been trying to develop a completely new catalog of music since we got rid of the Latin Mass in the mid-1960's. We are supposed ot encourage congragational singing, but a lot of our new hymns are too difficult for a congregation to learn (and they're often beyond the capabilities of our choirs).

We men in our church choir usually stand very close together when we sing, and we listen closely to each other and try to "lock on" to each other's voices. More often than not, the four of us sing with one voice, and it's wonderful. Our women are all afraid they won't be heard, so they fight each other to get close to the microphones. I tried to defeat that by using only one microphone for eight people gathered in a semicircle, but the women wouldn't buy that. While I was on vacation last fall, they dragged out another two microphones. So now I moved over to the women's side of the choir (and the choir director, a woman, sings with the men). I don't enjoy it as much as I do singing with the men, but it does seem to give the women confidence.

I think the best way to learn to sing in tune is to sing with other people in a circle, when everybody can hear each other well - listen for the sound of the blend of the voices, not just for the sound of your own voice (that's the idea I can't get across to our women - they want to hear themselves). I also find it's easier to sing in tune if you sing on the soft side - but it you sing TOO softly, you'll be like a plane that flies too slow and you'll stall and crash. If you sing too loud, you're sure to go off key.

Since I don't play an instrument, I often sing a cappella and often don't start songs on key the first try. If people are singing with me and try to correct things, it usually ends in disaster. You're better to stop and start over again - but sometimes people won't let you do that.

-Joe Offer-