1. Double-space all manuscripts and leave a one-inch margin on all sides of the page. (This is automatic on most computers.) Don't insert extra blank lines between paragraphs.
2. Use a header on every page. On the left, the header contains your last name, slant or colon, and your title. Put the page number on the right. (I put my header in 9-point font so that it becomes less distracting.)
It's not wrong, but I suggest you avoid putting the header on the first page. It's simple to do. On your tool bar, go to Insert. On the pull-down menu you'll see Page Numbers. Delete the checkmark that says to start on page 1.
3. Indent every paragraph half an inch. (Set your tab key. In Word, you need to hit the space bar 10 times to get half an inch.) Always use 12-point fonts. Many prefer non-serif fonts such as Arial. Don't use italics, or difficult-to-read fonts. Times New Roman (TNR) is the most common. If the publisher's guidelines don't tell you which font, TNR is a safe font.
4. Here's a giveaway of the tyro status: nonprofessionals insert the copyright symbol on the first page and some do it on every page. Editors know (even if writers don't) that the material is under common-law copyright when the piece is in a finished form. Using the symbol is a not-so-subtle way to say to editors, "I'm afraid you'll steal this so this is my warning."
Make your manuscript look professional
so editors can treat you like a professional.