The most important factor to consider when starting to build a business is the target audience. You have to think of who would you want to cater to.
It is not the most important, but it is a part of market research, which is very important. It is amongst one of the most important things that you should know.
Starting up and building a new business is a huge project that has many important parts, and to neglect one side and focus on the other aspect, thinking it is more important than the other, may mean the collapse of the business. For this I say that there are many important factors that will make a new business stand.