How I can practice and improve quickly to become a high level web developer

Answer 1

Is simple words there is no shortcut.
To became a professional web developer there is not only basic html,css,js

There are many frameworks of js and backend too is required to handle all this

Answer 2

Thanks, do you know where there are exercises to practice?

Answer 3

Udacity is a good environment to start from with doing labs and projects .Simple trick try to comment every line you code to have the habit of explaining your code to other or to yourself.