I like what Tony said about the weight training. You might want to think about doing some natural exercises until you are done growing--Push ups, pull ups, squat jumps. Search for some ideas from military workouts.
As far as motivation goes that should be simple. Picture yourself scoring that league winnng goal before you go to bed, when you get up and when you do your skill work and run. Your coach can make you and your buddies into a good team, but only you can turn yourself into a talented player.
Put your footwork into a routine. You should search for the 1000 touches articles. It is a routine of different fast footwork moves, moves to beat a guy and turns to do. Takes about 10 minutes to get 1000 touches. Sorry I don't have a link.
