Doug -- I know what you mean. There is a tendency to breath in & out in time to the bellows. Another temptation (maybe because melodies are so damned easy to pick out on the anglo) is to accompany yourself by playing the tune on the right hand (with chords/countermelody on the left) and just sing along with the tune. This can be a little monotonous, although it's good for chorus songs, so the audience have a tune to follow for their bit.