Any successful athlete, student, entertainer or professional will tell you : Goals are important!
 
Goals provide motivation, which are the fuel that inspire us to work hard in life and work even harder when we are tired.  Motivation is what gets us through difficult times, set backs and recoveries.  Without goals, we don't have any motivation.  If a student isn't motivated then this student will not achieve.  
 
Talk with your daughter and set some goals for the year that she (not you)  would like to achieve. Ask your daughter "what grade would you like to achieve this year?"  What grade would YOU give yourself for: not participating in class, not turning in homework, and not making your best effort."  Role-play that you are the student and she is the teacher.  How would she grade herself.  
 
Also, make sure your daughter participates in some clubs, sports or academic activities for fun, fitness, or competition.  Participating in school-sponsered activities helps teenagers stay motivated to achieve.  This can also include art or writing contests, band, chorus, spelling bees, student government, etc.  Participating in a number of these kinds of activities can help improve grades, confidence and leadership skills.