M is for...Margins! As an editor, I cannot emphasize enough the importance of margins.
This is especially important if you are sending out a paper copy of anything. If you are sending a resume to a potential employer, then you need to leave enough room that they can take notes. If you are sending a manuscript to a publishing company or journal, then you need to allow space for questions and suggestions.
If you are submitting electronically, it is easy enough to shrug and assume that the receiver will change the margins to suit their own preferences (if you are submitting a Word document). This is dangerous and could get you eliminated before you have a chance to compete. The publisher usually has a set of guidelines to help you out with margin size and will prove that you are serious about working WITH them.
No matter how you are sending out your work, it is important to leave ample space to make your piece easy to read. If the margins are too small, it makes your sentences and paragraphs look endless and leaves no white space for relief. If the margins are abnormally large, then it looks like there is nothing on the page. You have to find the correct balance to please the eye.