So, I am currently editing a novel contained in one of the most difficult, confusing, disorganized Word documents I've ever seen. Instead of using the centering button, the author has used the space bar to move the words over until they looked "mostly" centered. The line spacing is different throughout the document. The indent tabs are different throughout the document--and sometimes the author indents and then adds a few more spaces, apparently just for good measure.
Can you imagine me pulling my hair out over here?
When you're setting up a Word document, the best advice I have is to keep it simple. Set your default line spacing and indent before you write the first word--and don't change it halfway through. If you're not sure how to indent or center text, just keep everything flush with the left margin and let an editor help you with formatting later on.
As an editor, I would much rather spend my time working with you on your writing rather than your computer skills. Formatting can be set up very quickly...but correcting formatting errors can be incredibly time-consuming.
Be nice, and keep it simple.