The number one thing to consider is the founder him/herself. Is this person smart, hardworking, and ambitious? If the answer to any of those questions is no, don't invest into his/her venture. If the answer is yes, then learn more about the business idea, the vision, the potential for growth and profitability, etc.

Startups will always make mistakes. That's okay. But if the founders believe in what they are doing and have the work ethic, intellect, and a forcing driving them forward, chances are that they will succeed.

A face-to-face meeting with the founders is very useful.