When you lead group-singing make certain all members of the group have the opportunity to sing the very first syllable of the song, not join you half-way through the first phrase.
Establish the beginning tone and tempo prior to the first word. In the absence of an instrumental intro, hum the first note (choosing correctly for the song's vocal range). Always give a preparatory beat, in-tempo.
If they're not singing with you on the first syllable, you're not communicating!
Observe yourself conducting in a mirror. Learn superior techniques by studying the styles of effective song-leaders.
CONDUCTING Tip
When reading the rythmic notation of a musical composition, keep in mind that the composer had a musical inspiration, and then undertook the task of reducing his inspiration into music notation. While striving for mechanical reproduction of the timing, attempt also to "catch" the composer's inspiration.