Good question, one that many artists think about every day....how do I get better at my art? It is how we grow as artists, and the minute you think you've improved all you can, there is still room to improve even more. This is why making art can be a lifelong pursuit, even if you don't go into it professionally.
I worked with middle school art students, and they all wanted to draw like experienced professional animators, even though they were just barely teenagers. Many of them would copy Anime drawings or other cartoon drawings and get pretty good at it. However, I often had to remind them that, what they were copying was someone else's style, not theirs. It's fine to draw a really good Mickey Mouse or an Anime figure, but the question is, what do you want to say with YOUR artwork?
Along with improving your art skills, becoming better at your art means developing your art style and what you want to express with your art. So, practice, practice, and more practice. Keep a small sketchbook with you, and draw things you see that you like, draw or doodle ideas from your imagination, even draw from other artwork you like (but knowing it is someone else's style). Don't be discouraged if your art does not look "professional", or even as good as a classmate's. Don't compare yourself to other artists who have been drawing for decades, be happy with your work at this point in time. Many art techniques are skills, and the more artwork you do, the better you'll get at it.
What I found also sometimes helps young artists get better is not just practicing their art, but thinking about art materials they enjoy, and what they want to express with their art. Do you like to draw objects or places in front of you? Do you like to paint things from your imagination? Do you like to tell stories in your artwork? Do you enjoy painting or drawing people? Do you like drawing better than painting? Or do you like to make 3-D art? Do you love color, and so on. If you are taking art classes, think about the assignments you liked best. Knowing how you want to express yourself, and what you want to express with your artwork often gives you a purpose in making your art.
Also, look at other artists' work. If you live near a museum, and it is open, go there and see what attracts you. Most museums have online websites, that showcase their artwork. Google the National Gallery Washington DC, the Metropolitan Museum, New York, or the Museum of Fine Arts Boston. You can also look in art books at the library. If you are taking art classes, you could ask your art teacher for some suggestions of artists you might like.
Finally, a good way to get better is to listen to what your art teachers say about your artwork. Don't be afraid to show your art teacher artwork you do at home. I loved it when students showed me their artwork, since it allowed me to get to know them better and what they wanted to accomplish with their art. Your art teacher is a trained professional in not just teaching art, but in making art. So, listen to what your art teachers say and follow their suggestions; even if you might not always like what they say, try to understand that they are trying to help you to improve.
Best wishes! I hope this helps.