talk to people who have the problem you are trying to solve. Get inside their head, and understand their pain point. Then build a MVP to solve that pain point. you find these people thru forums, offline, networking, etc. it depends on what your product is - it is an entreprise app? consumer app?

Consumer app. We guess that we need to spend more time on 'getting inside heads' before doing too much more. If we better understand the pain points then we should have a stronger argument for building our MVP.

then you will need to validate 2 things: the concept and your marketing tactics. There are many consumer app ideas that many people would love, but if you have no way of reaching that, it'll all be naught. So you need to come up with tactics for marketing, whether it be getting bloggers to write about it, spreading it thru forums, SEO, etc, and test those tactics. See if they are viable long-term strategies.