When you know the recipient’s name, sign it “Sincerely yours” or just “Sincerely”, or in the US “Yours truly” is acceptable. Don’t try anything more cutesy or friendly unless a) you know the recipient quite well and are certain you can be informal without seeming disrespectful, or b) you have a “trademark” letter ending that’s part of your public persona (and the talent and popularity to pull it off). Signature and printed name: Signing your name is a minimal assurance that you stand behind what was written.
If you’ve done that well, they’re going to be asking themselves “How can I make this happen?”, which you answer in the last section of your letter by proposing an action they can take. “Call me at 鴔) 555 to arrange an interview” or “Let’s meet next Thursday to discuss this proposal” or “Order your copy today”. Don’t leave the action for your recipient to figure out. I think a lot of time we lack the confidence to ask for the action we want, and we give ourselves an “out” by leaving it unsaid, hoping they’ll figure it out themselves.