Do challenging projects. Read code from better engineers. Work with better engineers. Try new languages that actually solve technical problems instead of just having nice syntax. Contribute to open source projects that you use. Actually read the manuals that come with your tools. Notice when it's taking you a long time to do something and reflect on it to find a faster way. Constantly tweak your workflow to be more productive.

And the most important of all:

Get a split ergomech keyboard.