You can do this on Expert but it is far easier doing it on Hard. You are better off choosing songs that suit your voice than you are trying to work from a list of easy songs. In general though, you should try the zero dot songs first. If you are having trouble, hum instead and change the pitch of the note so that it is an octave up or down, since the game will allow for a “C” in any octave to substitute for the “C” in the song. You can also sing ahead of the note to try and hit the pitch before it actually comes up.