I've just finished arranging songs for my chorus' spring season. For the first time I realized that as I write out the harmonies in 3 & 4 parts, I'm just writing them the way I would sing them if I were harmonizing that part in the song. At first I was bugged by that thought, then realized that it may give a more "natural" harmony sound than if I tried to get all high-falutin' and choral sounding (look what happened to perfectly good folk songs when R. Vaughn Williams got to them- not that they aren't good arrangements, they just aren't folk music any more!). So, I agree with everyone who says- just listen to other people harmonize, and try to copy their style when among friends. If it sounds good, it is good!