some good advice already! I moved up a few years ago and what i found was the first year was just getting used to the longer distance and higher standard of racing.Then in your second and third year as a junior its your time to be at the front of the race.
With regards to training if you can ride with a faster/ stronger rider this will push you a bit harder and make training a bit more fun. if your not in a club or team try and join one.
Most of all enjoy it, A lot of youth and juniors loose intrest when cars,drinking and Girls come along.
good luck