In running copy, italicize URLs and eliminate the http:// if the URL begins with www.
The prospective student was referred to www.jhsph.edu.
Do not spell out United States, ever. Whether used as a noun or as an adjective, use U.S. (note periods).
He came to the U.S. in 1905 with the clothes on his back.
She buys only U.S. goods.
Use Arabic numbers for units of measure, unless the number is at the start of a sentence.
He ordered 3 feet of cloth.
The temperature was 99 degrees.
Ninety-nine degrees is a hot day in my book.