- Times New Roman Font, 12 point.
- Double spaced (You can get by with 1.5 but never single or more than double)
- No spaces between paragraphs of the same style
- Indentation by .25 (approximate) instead of using the Tab key to indent (more of a copy-editor preference rather than an agent or acquiring editor preference, but it's a good habit to get into and it never hurts to make your future copy-editor happy too).
All of these things can be found and set under the Home tab in Word by clicking on Paragraph. These basics will help make your manuscript look that much more polished and help give the first impression that you are prepared and professional.