first juice fast

Hi everyone,
I am about to embark on my first juice fast. I plan to do a seven day fast and I was looking for some advice. I am 27 years old and in good health, I want to know if I am likley to feel like I can go to work or not. I also want to know about doing the fast as well, is there as special type of juice to drink or should I drink only one type of juice, can I drink some tea or just juice and water. Any help with things like that would be appreciated.
By the way if anyone has any tricks for keeping wheat grass for longer than a week let me know.
Thanks for any help you can give me.
MIKE