A couple of things I like to do:
I'll go to a local bookstore and start browsing magazines. See what is being advertised. What is being talked about? Is there anything I am seeing over and over again (other than weight loss).
Spend an hour or two going through Facebook and Twitter. See what other people are advertising. Do some searches related to anything that catches my eye and see what other related products or opportunities I come across.
Go sit at a public place and just watch people. (If I paid attention to this one a few years ago when I was on Ellis Island I could have gotten in on the selfie stick craze early.) I'll go sit at a Starbucks sometimes and do this.
Watch the news or listen to talk radio. See what kind of problems and issues people are talking about. Right now privacy is a big hot button in the news. That could lead to all sorts of ideas such as VPNs.