Unless there is more specific information, the answers will be vague. However, all businesses need certain basic things. So, it will be a good idea to focus on these factors.
First, does your friend have the capital to start a company. In other words, does he have the money to pay the start up costs? This will be the first step. If there is no money to start the company, then nothing will take place. And if your friend has a good idea, then he will need to raise money.
Second, in connection to the first question, does your friend have a great idea for the business? Has he done the market research? In other words, does he or she know whether there are other businesses that do the same things. If so, this business might not succeed, unless they do something differently.
Third, it will be important to do a demographic study. For example, if your friend has a great idea, but it will only reach out to people of a certain age, then your friend will have to start that company in a place where that people of that age live.