I answered a similar question in this thread but will add a few things if there's an area you already are interested in. Look at the companies in the space that have received lots of funding from good VCs or have exited, and look up their scientific advisory board members. These are thought leaders in particular areas and are often very influential and networked. If you can build relationships with them they can point you to promising companies and proto-companies.

Also dig into the scientific literature (or hire a phd if you don't have a technical background) and connect with leading researchers in the space. Ask them about their work, and the work of competing academics. Do this enough and you'll find interesting science