When you're early in your startup, I believe that every single person that finds your site and signs up for whatever it is you are selling should be treated like someone that can refer you to 1,000 more customers.
So, during the earlier days of Tout, I tried to get a telephone conversation going with each and every person that bothered to sign up for my service.
It was easy, I just followed up on every signup (by a person I didn't already personally know) by sending them this email template:
New Customer Welcome
I used a Survey.io survey in this case, and then later on moved to a WuFoo form for more custom questions.