I know you're busy, but it would be deeply appreciated if you could take a moment to check on its status and inform me. I thank you for taking the time to check on this and look forward to your reply. An SASE is enclosed for your convenience. The first thing you should do is get to the point of the letter. However, keep it friendly.
Most editors are already busy and working as fast as they can.
Be sure to state the manuscript title and when you sent it to the publisher. Yes, you tell the address you mailed it to as well, especially if it's different from the address you're using for the inquiry letter. Publishers do move from time to time because of expansion or mergers, among other reasons. Try to always keep an inquiry pleasant. You'll get better results.