To say vocals are important in music would be an understatement. We want our vocal tracks to do justice to the vocalist’s talent and skill, but sometimes the recording ends up sounding muddy. There are a few tricks to clean it up at mixing time, but also at recording time. A lot of the problem comes from excessive low frequencies. Start by filtering out the frequencies below 100 Hz. Since the human voice tends not to be in that range, those frequencies won’t be helping your track.
There are more tricks to clearing up your vocal track here: http://www.audio-issues.com/home-recording-studio/question-the-answer-how-to-eliminate-muddiness-and-boomy-low-end-from-vocals