Three ideas:

1. Contribute to open source projects. And make sure you follow the style guide for that projects. (The style guides is often makes professional's code look professional.)
2. Come up with your own project, and it doesn't have to be a complete new idea, but if you try to create a real project, you'll run into problems or issues force you to learn new things.
3. If you haven't done so already, get an actual job where there are senior developers that you can learn from.

Get the basic concepts cleared first. By basic I don't want to say that you don't know JS.

Learn Closures - why they are helpful, how and when they can be used.

Mutation & Centralized states - why & when they are needed ( I'm not focusing on Redux or any pre-built tool , lets focus on the concept and implement it yourself in JQuery or plain javascript or Angular -- Your code will look a lot more clean & readable. )

Read others Js code, Read Npm modules , Checkout few open-source projects etc.

Checkout Javascript Ninja Videos ( They are very helpful in making you industry standard JavaScript developer )

Subscribe to Javascript topic on Medium , You will be continuously reading awesome JavaScript articles.