Everyone learns differently, so find the way you learn best. If you learn best by doing, you should do side projects, and they don't need to be novel ideas. There are tons of lists of project ideas (e.g. https://austinhenley.com/blog/challengingprojects.html).

Also, improvement can come at an accelerated rate if you have a short feedback loop e.g. a mentor or another person to work on a project with you, as opposed to going solo. It also helps with motivation.