Try to know about professor and his research field.Mention him with his proper designation like Dr/Professor. Donu2019t use Mr/Mrs.Letter should be 200u2013300 words not more than 3 paragraphs.Sample Letter are attached bellow. I hope that it will help.Subject: Meeting to discuss undergraduate research opportunities in topicDear Dr. Professor,I am a year student at university majoring in major. How you found out about the professor's research. Expression of interest in specific paper or topic. I would appreciate the chance to talk with you about your research in topic of interest and about possible undergraduate opportunities in your lab.My experience in research experience or class, confirmed my intention to develop my research skills and goal. I know you are very busy. We could schedule an appointment or I can drop by your office hours on day and time.I have attached my resume and unofficial transcript. Please let me know if there is any other information I can provide. I look forward to talking to you soon.Best,Name