Sing the songs you like. If you are enjoying singing them your audience will catch the love of the song from you. If you get the shakes Frankie Armstrong always says that if you deliberately shake all over violently for a couple of seconds the shakes lessen or disappear. I recommend that you don't do this in front of an audience or they'll be so hysterical they'll miss the song. Never give up singing, the human voice is the best and most portable of instruments there is.