For print submissions, keep the font at 12 point. I've heard many editors griping that their eyes can't handle anything smaller. Courier or Times New Roman - anything else comes across as unprofessional. Underline to show italics (easier to see on the page). Name, address, e-mail in the top left corner. Word count (for a short story) in the upper right. Title about halfway down the page.
For e-mail submissions, it gets much trickier. You're better off reading the formatting guidelines of whoever you're submitting to, since this varies so much.
And it goes without saying, if an editor or agent or publisher request a specific format, ignore everything I've said and do what they tell you.
Yeah, some folks won't care. Some will. Don't obsess about it, but do take the time to make sure it's a professional-looking manuscript.