Using an IDE which knows how to follow references and show types.
Replacing password with keys, and placing those in an authentication agent.
Setting up shell to complete commands from history on a single button press (I'm looking at Debian, which doesn't do that).
Arranging windows across virtual desktops and switching them with keyboard shortcuts is quicker than alt-tabbing.
Keeping progress as a series of commits in git, even when just exploring. When there's a need to take a step back, just restore an earlier commit. They don't even have to work to be useful.
Taking breaks from coding to think about what should be coded and how.