Trying to add a few bullet points that other's haven't already mentioned...
Learn your build tool of choice well. You'll be amazed at how much time you save when you know how to automate your repetitive build tasks. If any given build process takes more than 1 shell command, you're doing it wrong.
Be able to read and understand code written in a language you've never used before. Many times when solving a problem you'll only find snippets in other languages, but you've got to learn how to translate that to your own when no examples exist in your preferred language.
Conventions are great and considerably cut down on development time, but make sure you know what's going on under the hood as well. Don't just blindly accept the convention as a black-box, because that's the surest way to introduce subtle bugs that are difficult to squash.
Learn how to quickly adapt to change. Your career will find you constantly trying out new frameworks, new languages, new development environments, new project teams, new managers, new development and project-tracking styles.... make sure you are able to keep up and get productive quickly no matter your new situation.
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Trying to add a few bullet points that other's haven't already mentioned...