Well... It depends what type of expression you are using. For instance, raising your arms high above your head might be expressing being proud or overjoyed. Your facial expression matter too. If you were to have a gloomy face on because your having a bad day; please ask the director or teacher to let you sing sad song. If it is happy song it will send people a negative message since you are to solemn to move the frown upside-down. Having your hands facing upwards with elbows gradually raising may express confusion or laughter. As you might be able to see now; every expression and movement you make needs to match up with your song so that people get the message and story that you are telling.