In the Facebook-dominated world of the modern web, data collection has become highly opaque. When you share an intimate thought about a dying friend over social media, that sensitive, personal data becomes a commodity that is sold to marketers of flowers and books on death, when you Like a band in a social media environment, you (often unwittingly) sign up to get offers for tickets when that band is playing near your city or town, and so on.
I am being harsh on the opacity of online "sign up" technology to make a point. As someone building your own site, you can instead, make the collection of data voluntary, conscious, and transparent. People who sign up, on purpose, for your e-newsletter, your announcements, your special offers, and so on are—after all—likely to be more receptive to getting mail from you than the ones they did not consciously ask for, but that were generated by their activity on Facebook, Amazon, and so on.
So how do you collect information...