A few years ago I printed the manuscript guidelines from the website of Harris, Harris & Donahue Ltd. and I tend to stick to them. They are:
MARGINS: 1.25 to 1.5 inch - adjusted to allow approx. 10 words per line
TYPE FONT: Courier or a similar easy to read non-proportional type style
TYPE SIZE: 12 point type on a computer
TYPE STYLE: Plain text throughout - underline words that are to be shown in italics in finished novel
TEXT SPACING: Double spaced, no additional lines between paragraphs. Top and bottom margins must be set to allow 25 lines per page (not including page header). Turn off 'windows and orphans' feature if using Microsoft Word.
ALIGNMENT: Flush left NOT justified
HYPHENATION: Words at end of line must not be split or hyphenated
SENTENCE SPACING: Double line spacing
PARAGRAPH INDENTATION: Initial word of each paragraph indented five spaces
PAGE HEADERS/TOP MARGIN: Every page except the first should contain the authors surname (lowercase), a slash and the title of the work (uppercase) at flush left in the header. Flush right should be the page number on the same line
THE TEXT: The first line of text should begin 1-1.5 inches from the top of the page
CHAPTER HEADING: A line of type, centred, in uppercase placed a third of the way from the top edge of the page (3.5 inches). Chapter number should be in words not numbers
TITLE PAGE: Authors real name, address, telephone number and e-mail address should be shown top left of the page (single spaced lines). The title should be centred, 5 1/2 inches from top edge of page and in uppercase. Second line below the title should be the word by followed by the authors name on the fourth line (shown as it would appear when published).
WORD COUNT: Do not use the computer word count, use the approximation of 10 words per line, 25 lines per page giving 250 words per page. Half pages or less are considered to have 125 words per page.
I hope this helps you as I have found it very useful. One other piece of information that may be of interest to you is that a book under 50,000 words is considered a novella and most publishers will not even consider these.