Advice on how to approach a professor about working in their lab
It can be quite competitive to secure a position as a graduate student, an RA or even a volunteer in a lab. Most profs are bombarded with more emails per day than they can possibly answer, including many from prospective students. The generic messages like "Hi, I'm interested in your research, are you accepting students?" are likely to go unanswered. So make that critical initial email as strong as possible.
Select the professors whose research interests you the most, carefully read their web page and some of their papers, so that you are well informed about their research.
Write a very brief email to each one. No more than 1 or 2 short paragraphs. Keep it professional. Use a meaningful subject line like "Prospective graduate student interested in your work on XXX". Use an appropriate title to address the researcher, e.g. Dr. or Professor (NOT Ms, Miss, Madam, Mrs, Sir or Mr). Do not address them by their first name unless you know the professor personally and they have told you to call them by their first name.
Express your interest in their research, and mention one or two things you read about in their work that particularly drew you to their lab. Avoid generic statements like I'm interested in memory, or cognition and ageing. Say something that shows you've taken the time to read their papers.
If you have research ideas of your own that you'd like to work on, state that. If you are flexible about working on a range of projects within the professor's research area, then state that too.
Mention very briefly any relevant background that you have. Ideally this should be specific to your target lab's research area but you could also mention general research skills e.g. knowledge gained in relevant courses, experience or coursework that gives you skills in statistical analysis, computer programming, any research-intensive courses, any volunteer or thesis or independent study courses that gave you research experience.
Include your CV and transcript as attachments. If you don't feel that your overall GPA/transcript reflects your true abilities and potential, include a very brief explanation of the reasons why, and list your best grades in the most relevant courses in your email.
Proof-read your message very carefully. If you have been sending out a generic letter to many labs and just replacing a few keywords (ignoring all of the above advice), your recipient will likely know it and will treat your message like another piece of spam in their inbox. If you forget to replace the most important keywords like the name of the Prof, their department or their lab or their reseearch area with the correct one, the recipient will very likely assume your message is spam.