Joey gives great advice. Also another great teacher to use is Paul Baloche. His website
http://leadworship.com has helped me tremendously, and you'll be surprised how much of his music you already know. Live, eat, breath Worship music. Paul's site also has
free songbook downloads that are awesome. Use every resource you can think of, and learn from those true worshippers, those Chris Tomlin, Paul Baloche, Kari Jobe, Matt Redman worshippers out there. Go to youtube and view some of their songs and get an idea of what you like and don't like, what your team and congregation will maybe accept, and give it to God.
On the other hand, do you feel called to be the Worship Leader? If not, let your Pastor now that you'll fill in for the interim, but that you don't fell that calling. Just because you are "bumped" into a position doesn't mean you should be there, and just because you can do it, doesn't mean you are called to.
Be encouraged and enjoy this time! Leading worship is joyous - not only do you help usher people into the holy of holies via music and song, but you can know that you are filling the throne room itself with praises from below! God Bless!!