First impressions count. That's why you need to carefully write your first autoresponder message. It is the first impression your list members will have of you. Even if they really liked what your website had to say, they will unsubscribe very quickly if they don't think being on your list will offer them a lot of value.
Your first message should almost never contain a sales pitch. This is your chance to prove that they will want to remain on your list. You want to be warm, open, and friendly. You should also consider offering a special bonus or surprise for free.
This will immediately help set a positive association with your messages. This can increase the open rates on your emails, put your relationship on the right path, and help you make more sales later on.