Startups don't win because of a great vision, but because of a superior strategy. If you want to have the superior strategy, you must simply have a better customer insight. Customer discovery principles can help you to get real insights about your customers.
The first rule is to fall in love with a problem, not your solution or business idea. You must have a clear picture what your product is hired to do. With customer interviews and different types of tests your job is to prove value hypothesis (that people are prepared to pay for your solution).
You can write down all your hypotheses on business model canvas, running lean canvas or even in a spreadsheet. Then you have to constantly sketch out alternative business models by asking yourself difficult questions and testing different assumptions.
Steps to customer discovery include developing a vision, setting the hypotheses, getting out of the building and performing a reality checks. The best way to start the customer discovery process is with the riskiest assumptions.
Important tools that can help you with customer discovery are also segmentation, personas, empathy map and value proposition canvas. After exploiting all the tools you should have a clear picture what are your customer's pains and gains and what are they willing to pay for.
When you are doing the customer discovery interviews to get the market insights you have to avoid doing any behavior predictions or being satisfied with compliments, opinions or stalling. What are you looking for is a real commitment from early-evangelists.
Remember, wrong assumptions are mother of all fu*ck-ups, and with customer discovery you can make sure you are not building your business based on the wrong assumptions.