My grades are so bad. Please help?

[Blah]

Hello, I'm a freshman in high school. And I'm struggling a lot with high school life. My grades are horrible, please don't make fun of me. I'm really smart, but I don't put effort to do my homework. There are so many distractions, like Facebook, Twitter, Tumblr, etc.. I tried deactivating Facebook but I just keep ending up reactivating it. But anyway. The 4 basic subject classes I'm taking are: Comparitive Cultures, Algebra I, World Literature I and Earth Science. Then there's Spanish, Freshman P.E. and Video Communications. Currently these are my grades...
Comparitive Cultures; B- (81%)
Algebra I- D (66%)
World Literature I- F (59%)
Earth Science- B- (82%)
Spanish- C (75%)
Freshman P.E.- B+ (88%)
Video Communications- B+ (89%)

~ how should I schedule my homework? Because I can't play sports because of this thing called a "C" rule. And how do I keep myself away from Facebook, Twitter, Tumblr, etc...