I was reading Jeff Atwood's book Effective Programming, which is based on his excellent Coding Horror blog, and came across a great suggestion.
Git clone projects that you use. Reason - if you encounter a problem while using some third party project, then you will better understand how to debug the problem. You might be able to find and fix bugs in the third party project, but you might be just as likely to learn how you are using some other code incorrectly.
One step further - git clone interesting projects. Reason - see how other people code and how it differs from what you do. Think about why you like some bit of code or why you don't like it. The important thing is to have an opinion. You can always change your mind later.
I've sort of been doing this, but I'm going to try to be more methodical about it now. It seems like a great way to learn, and get faster at diagnosing root causes of bugs.