The best way to improve with your art... Is to keep making art! Keep all your sketch books and work, because it's great to look back on and see how far you have come.
Lately I've been trying to create some new little characters and it's been really fun learning new techniques and ways to make things. YouTube and Pinterest are full of all kinds of tutorials for what ever kind of art you want to make.
Have fun creating and I hope some of the little tutorials on the site help you.
Below is a little mouse I made using Lisa Glanz brushes for the Procreate app, on the iPad