This is a wonderful classic and you can do so much with it, working on conditionals. Give the students the song title "if" and let them brainstorm what the song could be about. Write their ideas in the board.
Play the song ( lyrics are simple and repeating - no unknown vocabulary)
Discuss with your students how it could be a better world in all aspects (health, peace, environment, relationships etc)
Let students complete the sentence "if it weren't for this......"