To borrow a quote from Wayne Gretzky, go to where the puck will be, not to where the puck is now.  Don't pick an idea for today's market because there are likely to be lots of competing solutions that are further ahead than you.  Anticipate a problem that will existing in 1-3 years time and then you'll be ahead of the curve.

The best way to come up with ideas is to talk with prospective customers.  Most will freely tell you their problems.  We also draw inspiration from online trade publications and bloggers. (I've grown very cynical of what I read on the web.  Most articles and vendor claims are greatly exaggerated or intentionally leave out flaws in their solution.)

Conferences are often a good way to quickly get educated, evaluate trends and study competition.

Many thought leaders will publish trend articles and reports on how they see the industry evolving.

As you think up ideas, evaluate and filter them against a set of criteria.