I’m probably years behind everyone else on this, but I just learned about the compose key.
I’d always wondered how other people who used the Latin alphabet—French-speakers in Canada, even—were able to write accented characters like à or é, not to mention people further abroad who needed the Icelandic þ or Turkish Ş. European keyboards have different keys on them, but did people with American keyboards always copy and paste from somewhere else? In Emacs I use the Ivy, Swiper and Counsel package that lets me use
counsel-unicode-char (bound to
C-c 8) to search for any Unicode character, and
C-x 8 RET is a built-in command that does the same. But I don’t want to copy characters from a temporary Emacs buffer into a web browser.
Happily, on Unix systems it’s easy to get this going. On my Ubuntu machine, Gnome-tweaks lets me set up a compose key. I made it
[Right-Alt], which I never use. Now I can hit
[Right-Alt] o c to get © and similar combinations to get many other combined characters.
I am now able to use proper em—and en!—dashes in my emails, and when I put in footnotes with URLs I can use ¹ and ² instead of bulky old  and .