When you receive a message from a potential employer, you should first review their profile to ensure the position is a good fit. Make sure to read the whole thing so you do not miss any important details.
If you do not feel the position is a good fit for you, then respond to them saying as much. Be sure to be polite and courteous when responding. A message like the below is an example of what you could say:
“Thank you for your interest, but I do not feel this position is a good fit for me at this time. Good luck with your hiring search!”
If you do feel the position is a good fit, respond to them citing your interest in the role and how you think you might be able to help them. It is also great to get the ball rolling by offering to set up a call or in-person interview so you can discuss the role further. A message like the below is an example of what you could say:
“Thank you for your interest. I would be very excited to speak more with you about this position. I’d love to hear more about your needs and discuss my qualifications with you in detail. Are you available for a call sometime in the next few days?”
NOTE: It is very important that you respond whether you are interested or not as it shows good etiquette. It also offers the employer closure so they can move on in their search.