Only ask your visitors for their email address when they sign up for your newsletter, so you don't scare them off. Once signed up, show a “Thank you” page to the visitor. First at this stage you ask for the additional information. Now an important part; give the visitor a compelling reason to fill in the extra fields. There has to be something in it for the visitor and not just for you.

If you feel curious try signing up for my newsletter and see how I approach the conundrum - making the visitor (you) part with extra information, without stopping you from signing up.