A lot of people will recommend reading great code -- well known open-source libraries etc. That's good, but one thing I think is useful is to read your dependencies. Then you can get a better picture of what "regular" code is like. Most popular libraries are not great to read because they are often very abstract, or they use so much helper code that it's hard to see what's actually going on. But fairly small libraries are usually easy to understand and usually are also fairly straightforward, but by reading code you'll be able to put yourself in the shoes of someone who will be reading your code one day, which is the most important things to keep in mind.

I'm mainly a front-end developer, and the nice thing about the npm/node ecosystem is all of your dependencies are right there in node_modules, so feel free to read them to see how they work, or why something isn't doing what you expect -- you can even add debugger statements or console.logs.

In some ecosystems this is harder because you might have to hunt for the source, or only have headers. For example in ruby, use bundle show my_dependecy to see where the code is stored.