I've been involved in advising a large number of startups over the past 10 years. I've seen a some of them receive investment from a variety of sources and many that did not end up landing investment. I've also invested in a number of startups myself as an Angel Investor.
I think we can break down "investors" into three basic categories. (1) Friends & Family; (2) Angel Investors; (3) VC / Institutional Investors. Depending on what stage you or your startup are in, I think you can look at them all in the following way:
Friends & Family
If your product does not have much business traction (a fast growing user base and/or a growing amount of revenue) and you yourself do not have a track record of building and exiting from successful startups, then Friends and Family may be a good option for you to consider. Friends and Family will invest in your startup because they believe in and like you. They will not be nearly as concerned about actual business traction as Angels and VC will be. They love you, they want you to succeed, and they are more likely to believe in you in spite of a lack of history.
Angel Investors are looking for some form of validation either on the business idea, product, or you as a founder. A sophisticated and professional Angel Investor may have a number of criteria that they are looking to see met ranging from potential market size, growing / shrinking market, strength of competitive advantage, track record of founders, evidence of product/market fit, revenue, the passion of the founder, etc. You need to think about creating a strong case to convince Angel Investors to invest in the startup. The evidence should be more than your personal passion for the idea. I think many Angels will take more risk than VCs and Institutional investors, but you should definitely have a primetime real investment opportunity here.
VCs / Institutional Investors
These type of investors are looking for a proven and validated business model that is ready to be scaled. Some are looking for $10M businesses that can be scaled to $100M businesses. Others may be looking at more early stage ventures that have a very strong competitive advantage in the marketplace and the potential to grow very large very quickly. In some cases, I think we've seen some VCs invest in founders in the idea stage, but this is generally an exception rather than a rule.