Understanding default file copy operation behaviors is important. But so is understanding how you can work around these defaults to ensure that you always do what you mean to do. There are many ways to do so, including interesting Cut/Copy/Paste options that mimic how we work with documents. But for purposes of this tip, let's stick with methods that work with drag and drop.
Force copy. To copy a file regardless of the source and target destination, hold down the CTRL key while you drag and drop.
Force a create shortcut. To always create a shortcut to the source file, hold down CTRL + SHIFT while you drag and drop.
To always get a choice. To get a pop-up menu of file operation choices, drag with the right mouse button instead. When you release the file at the target location, you'll see the following context menu appear, with Copy to, Move to, and Create shortcuts here choices.