The three links @iamknox posted are really awesome learning material, especially the first one. I love Kyle Simpsons books and videos, he explain’s JavaScript in a very different way and is extremely thoroughly with it. I learned a lot from him.
If you didn’t start already, learning EcmaScript 2015 (ES6) will help you write cleaner code, as this is a newer version of the JavaScript standard with many new language features, such as a different function syntax. I find this a lot cleaner, here is a simple example:
// Old syntax
fs.readFile('file.txt', function(err, content) {
console.log(content);
});
// New syntax
fs.readFile('file.txt', (err, content) => console.log(content));
There is more of course, just to get you an idea.