You should avoid any material that puts a great demand on your voice from a dynamics standpoint. Select songs that are more melodic, not those that need “punch” or require a “dramatic” dynamic level. As I’ve said already, singing songs is not vocal technique. Just because a teacher encourages you to “sing out,” or gives you hints on how to interpret what you sing, does not mean you are learning vocal technique. Style and interpretation are no substitute for vocal technique. Without good vocal technique, style and interpretation are greatly restricted.