[pfitzsimmons]

For a B2B product - identify five people to whom you can honestly say: "You would be stupid not to buy this product" These should be real people you can name - not hypothetical people. If you cannot identify such people, but think they are out there, do everything possible to find them. Go through Linkedin and see who in your extended network fits your target market and find someway to talk to them. Email people or message people on blogs or social sites that seem to have the pain point you have identified. In reality, you will need to talk to far more than five people in order to narrow it down to five people who clearly need your product.

Once you have found a set of people who need your product, get their feedback on the idea, show a mockup or prototype, and ask if they would buy it. If a bunch of people say "yes", time to go build! But as you build, make sure you check in very regularly with potential customers, so that you stay on a the right track.

Keep in mind there is a big trap you must avoid in this process. Many prospective customers will be positive about an idea, but they overestimate their own willingness to get through the friction involved in adopting a new product. So the prospect says the idea is good - but then you build it, and they don't actually use it, because turns out email and excel had a bunch of hidden benefits that make them better than your product.

As an entrepreneur, you need to implore people to be brutally honest in their feedback, lest you build the wrong thing. You should focus more on identifying their pain-points than on pitching your own solution. You also have to make your own judgements about how big the pain point is, rather than just blindly trusting a prospect when they say they would buy your product. And you should to some extent reverse pitch - ("Did you think of solving your problem by doing X? Do you really need me to build a product to help fix this?")