If you’re sending it to an agent or publisher, look at their website for submission guidelines. Most will have their formatting preferences posted. Follow them to the letter. If you don’t see any guidelines, here are a few that will help your manuscript look its best.
Assuming you’re submitting a Word document, select all and go to the Page Layout tab. Under Paragraph, choose Indents and Spacing. Under Indentation, set the Left and Right at 0 inches. Under Special, choose First Line. The default of 0.5 inches is fine for a manuscript.
Now look just below Indentation and find Spacing. Set both Before and After at 0 point, then set Line Spacing at 1.5 lines. Any numbers that were in the box under At will disappear. This is fine. When you’re done, click OK.
Of course, don’t forget to run spellcheck and make sure you’ve made all the revision necessary to tighten your story.
Put a title page on your story with your contact information. Include your email, phone number, and address. Some publishers/agents will also require your word count, genre, and so on.
This presents a clean file that looks presentable and is easy to read.