I don't know about anyone else, but I find it incredibly annoying that the Microsoft Word doesn't use F3 as the shortcut key for finding the next occurrence of something that you have previously searched for. It's an unwritten standard across a huge number of windows applications and I find myself pressing F3 in Word out of habit.
The Correct (out-of-the-box) shortcut key
When you are working on a document and need to find text (a specific word or phrase), pressing CTRL + F pops up the “find” dialog box and lets you search for that text. Now, let’s say you found it and kept working on that document, and now you want to find the same text again. Pressing CTRL + PageDown will instantly take you to the next instance of that text! No need to open the “find” dialog box again (Keep CTRL down and press PageDown to move to the following instances of that text).
Changing the shortcut key to F3
To its credit, Word allows customization of its keyboard shortcuts. Unfortunately, I just could not locate the “FindNext” keyboard shortcut in Tools -> Customize Keyboard to apply customizations to. Turns out it’s actually named “RepeatFind”, as opposed to “EditFindNext”, which you’d expect when the “Find…” command is simply “EditFind”.