Git: Revert file to master
The same approach applies to any branch, but reverting a file to its state in master seems to come up most often.
Firstly, in case you need to list which files have changed between your active branch and master:
git diff --name-status master
Then to revert the file to its state in master:
git checkout master path/to/file
At this point, the file will already be staged, so if you need to unstage it:
git reset path/to/file