Pretty advanced for a first animation!
There are some V's drawn into the hair design that sporadically pop in and out of existence
Watch the backpack strap in the bottom right- it'll disappear and reappear, and it unintentionally jiggles with the motion.
There's a line along the neck/throat that disappers and reappears sporadically as well.
Other than that, keep consistency in mind and make sure your character is staying on-model. There's nothing wrong with exaggeration, squash and stretch, and overall flexibility, but be cautious when their proportions unintentionally warp. That'll come with practice!
Check out Richard Williams' "Animator's Survival Kit" its a book you can find as a free pdf online, and it contains a wealth of information about animation. Put into practice, your skills will advance.