• Start with Dear Prof./Dr. <Name>, internationally, they don't prefer being called Sir/Ma'am as that sounds generalized. And, especially in the US, Sir/Ma'am–culture is often frowned upon. 
• Keep the email as short as possible. Not very short, not very long. Try to keep it within 300 words and 3 paragraphs.
• In the first paragraph, try to introduce yourself.  Your current academic affiliation has to be included here. After going through this, the professor should feel that you are writing to him/her for a graduate position in the lab. It would be best if you write this explicitly. 
• In the next paragraph, mention your research interest and why you like this field. You can mention the papers you read about the lab. This will definitely attract their attention. 
• Finally, list your relevant skills, coursework, and how you would contribute to the lab if given a chance. Thank him/her for his time and direct them to your CV. Ask them if they would like to have a Skype call with you or continue the discussion over email. 
• Use a simple subject line for the mail e.g., "Prospective Graduate Applicant–Fall 2025".
• Be SPECIFIC!

 The Most important part: USE YOUR OWN CREATIVITY