One of the most useful tools in Android's Eclipse plug-in is the Layout Editor. It is easy to experiment with layouts using the drag-and-drop enabled editor without having to worry about the correct syntax or if you are using the correct attribute name.
After creating your layout this way, however, you can end up with a messy XML file. I say "messy" in the sense that elements can run on in one veeeeeeeeeeeery long line, and if you are about to edit the XML file manually, this can be a nightmare.
I used to format the XML file by hand, putting in line breaks and correcting indentation. But one edit using the graphical layout editor and it's messed up again. And then I had a light bulb moment. Eclipse allows auto-formatting of code, but what about XML files? AHA!
It turns out that auto-formatting works for XML files too! Simply select all the contents of the XML file (CTRL-A) and then press the ultra magical shortcut CTRL-I and your XML file is clean and orderly as can be! YAY!