Some of the simplest tips are also the best. Years ago, I learned a simple keyboard shortcut that can undo the last action—Ctrl+z. It’s similar to the Undo Typing feature, but allows you to keep your hands on the keyboard. Initially, it doesn’t seem like such a big deal, but I use it all the time and find it invaluable.
Most frequently, I use it to undo Word’s default curly quote when writing snippets of code. If I retain the curly quote and a reader copies the code into a VBA module, that curly quote usually throws an error and the reader hasn't a clue why. After typing the single or double quote (‘ or "), I press Ctrl+z to remove the special formatting, which leaves a straight quote character (' or "). The key is to remember that this shortcut erases the last "action," which isn’t always the last character entered. In my case, the shortcut deletes the formatting and not the actual quote character.
I run into new uses for this all the time; I hope you’ll find it as useful as I have. By the way, the keyboard shortcut for repeating an action is Ctrl+y.