Say if your doing it for your company you would do an idustry analysis and check the competition in the area. Check other companys benchmark how did they suceed or fail?
You would research the demographics of people wanting the product or service. Are they being targeted? Can they afford the product/service?
Is your product or service going to sell? Forcast sales see if your going to be profitable many many things go into market research in many different ways there are a lot of answers for this question.