When singing in musicals, you have to perform in a heightened manner in order to be able to launch from speech into song. You can’t speak at your normal level and then jump into song and expect it to be credible. In rehearsal, try muttering to yourself before your lines come up, so as to build up your energy levels before it’s time to speak. Then speak with more energy as you come up to a song. You’ll probably be speaking over a musical introduction, which will demand this energy anyway.
The old cliche is that you sing when speech isn’t enough, and on stage we have to believe that there’s a need, at a certain moment, to sing. Take the line from the musical Anyone Can Whistle: “Everybody says don’t walk on the grass/ Don’t disturb the peace/ Don’t skate on the ice/ But I say do.” What the character J Bowden Hapgood is singing is essentially “break the rules”. But, behind that sentiment, the actor should have a whole internal list of reasons for why he is singing this: because he’s lived life as a political dissident, because he sees the woman he’s singing to as stuck in her ways, because he fancies her too, because he genuinely wants this for her and because she probably could achieve it. All of that personal history and information about a character’s intentions should be in the performer’s head before singing the line “But I say do”.
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