Juggling balls is the last thing you need to practice to become the best you can be. Im 16 and i've been playing soccer for 6 years now. I'd say condition. The avg soccer ayer runs 6 miles or more in a game. So you need to condition your body to run alot. I reccommend going for light jogs everyday and running distance as it gets easier. I do just 2 miles every day to get me ready for my high school season. Also get a a ball and work on your touches. Use cones. Work on your weaker foot. And controllig the ball. Also, if you can.. Go to the nearest park with a goal and work on your shooting. Never give up. Work hard every day! You will get better with determination. Just 10 minutes of touches every day can make a difference.
Outlet paper gives a good answer about juggling. While juggling helps with ball control, its not an actual match skill. No one goes up the field in a game while juggling the ball.
I would recommend that you concentrate on match skills such as passing, trapping, shooting, and dribbling. An internet search will reveal many drills you can do by yourself, or with a small group of friends.
Practice juggling balls....