Water with a little lemon works good for me before I sing. If you are just getting started, it's ok to do covers...how else would we practice? However, when you sing a cover, try to make it your own sound. Sing with your natural voice and never try to imitate someone's voice. I've even taken songs and changed the genre but kept all of the same lyrics. For instance a country song transformed into an R&b song or vise versa.