This says it all.  Great Model for how sing and get others to join in singing.

As repeated from Sociability Songs Copyright 1928:

Community singing and group singing has become securely established as one of our essential social activities.  The real value of music in a group singing lies in its power to lift all of the individuals into spirit of unified interest in some worthy cause. Singing together creates an atmosphere of good cheer and good will and stimulates courage through the sheer joy of self expression.  All love to sing if they can only be persuaded to join the others.  The group will sing some simple, beautiful song or some humorous, senseless ditty will be better prepared for any kind of unified action.

THE LEADER- The prime requisite of a successful leader is enthusiasm and the ability to inspire.  He must have a sense of rhythm, however, and sympathy with the group whom he is leading.  A good sense of humor is more important than knowledge of music.  Ordinary mistakes should be made part of the good spirit of the evening, for good nature and humor will be more effective in securing a response from the group than fault finding.  Encouraging compliments of the singing will mean improvement.  When a leader cannot be secured, a good pianist may secure the desired results.

THE PIANIST- The accompanist can easily determine the success or the failure of group singing.  The piano is often the dominating influence in the singing and should be the first to catch and suggest the spirit of the leader and the occasion.  Firm and musical tones are far better than noisy keyboard gymnastics.  The piano must often lead but it must not lead too fast.  It should never drag.  The pianist who drags will quickly ruin a social sing.  The piano should always be placed so the leader can be seen easily by the pianist.

Practical suggestions: 

1.  be sure to make out a list of songs which you expect to use, always beginning with the most familiar songs which all can sing.  A good beginning is always important. It is usually wise to let the group suggest some favorites.  This will help them to feel that it is their meeting.

2.  Make a special effort to secure the attention of the crowd before you start a song.  All will enjoy the singing better if there is a good start.  Watch the singers and try to encourage those who are not doing their share.  Some who cannot sing may make a definite contribution by whistling.

3. In singing the rounds are sure that most of the singers know the melody.  It is well to have all sung the entire melody before dividing them into groups.  Be careful in your directions as to where each group is to begin and how many times the round is to be sung.  Contra Singing nay be of even more interest to the crowd than rounds---- one half of the crowd sings one song while the other half sings another.