If you're still in school, my advice to you for now would be 90% to just draw what you love and have fun! Cultivating a love of drawing is what will see you keep making art long-term, so enjoyment should be the centre of gravity when learning anything creative.
With that said, if you want to improve quickly, there are certain things you should practice. Chief among them is drawing from life. I'll give you an instruction to follow as you create: Whenever you need to draw something new, try drawing a few realistic versions of it from a few photographs. Then draw it in whatever style you like to use. (Anime, western comic, whatever.)
That's it, that's my whole advice. That's enough to begin with.
There's much, MUCH more to learn, but the last thing you need as a beginner (with any new skill) is to be overwhelmed with too much information. Just start drawing, and have fun!