times new roman 12 point font and single spacing is probably acceptable as well as double.
Yes, the paragraphs should have one blank line between them. This is especially important when using the block form of letter that has no indent at the beginning of the paragraph.
Formal language is the most appropriate language when writing a business letter.
When writing a business letter it is proper to include at least two sentences in each paragraph.
The first sentence (paragraph) of a business letter should state why you are writing (the purpose of) the letter.
That would be the "body" of the letter.
Always leave a blank line between each paragraph of a business letter even if an indent is used to begin the paragraph. Each paragraph of a business letter has a specific purpose*, the blank line acts as a pause for the recipient to think about what was just read before moving on to the next paragraph. *If each paragraph in your letter doesn't have a purpose, then you need to edit.
Yes, the paragraphs should have one blank line between them. This is especially important when using the block form of letter that has no indent at the beginning of the paragraph.
First paragraph
Formal language is the most appropriate language when writing a business letter.
When writing a business letter it is proper to include at least two sentences in each paragraph.
The first sentence (paragraph) of a business letter should state why you are writing (the purpose of) the letter.
The body of a business letter, or most letters for that matter, should be single spaced. However there should be a double spacing in between each paragraph. (Don't forget the special spacings in certain areas, such as for signatures and after mailing information.
That would be the "body" of the letter.
introduction
sincerely
It should succinctly state the purpose of the letter.
2 spaces