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. Who are the communities that you may profit off of. Like for example if there is a school near you, you should know that students would be your target audience. You should start a business where students can buy materials from or a place they can study or even hang out around. I believe that if you studied your target audience, the first step of your business is already successful enough.
Yes target audience is very important but it is not as important as the money needed for the business to launch. So, in my opinion, the most important factor to consider in building a business is the monetary flows, both the inflow and outflow. Without proper financial management, any success in business will be ruined due to overspending.
I have seen lots of successful businesses go bankrupt due to failure in managing their finances. They have targeted the right audience, produced the right products, but failed to manage their production and promotion, thus wasting too many funds, but got less in return.