My advice: get a github account, start a repo and build a static site with HTML, CSS, and JavaScript. Build a fun site with your experiments. Or you can go to sites like Coderbyte which send you challenges. Alternatively, go to Codepen every day - clone a fun demo someone wrote, and teach yourself how to write it in your own style. Basically - set up a environment where you are exposed to code daily, and you have to write code in response. ... Otherwise known as a web development job :)
If you really want to get knowledgeable, go pick up some simple JavaScript gigs at Fiverr and just start doing it.