Some people use double spaces (including me once) for indenting their code. However, in Dreamweaver, it is much more powerful to use tabs for this reason:
You can highlight an entire block of code and press the tab key to indent the entire block. Furthermore, you can remove levels of indenting on a block by pressing "shift-tab". Very useful for making modifications to large code, while retaining indenting.
Also, remember to decrease the width of tabs by going into "Edit > Preferences > Code Format" and changing tab-size to a smaller number, so that your code stays as compact as double spacing.
