20 Ways To Say No (to over working and doing stuff you dont want to do) by Ramona Creel and found at life hacker.
+ I HAVE ANOTHER COMMITMENT - it doesn't matter what the commitment is.
+ I NEED TO LEAVE SOME FREE TIME FOR MYSELF - it's okay to be selfish.
+ NOT RIGHT NOW, BUT I CAN DO IT LATER - if they can't wait for you, they'll find someone else.
+ NO - sometimes it's okay to just say no!