From what I see, mostly succeed ICOs out there advertising their brand through google ads, twitter, and facebook campaign, also Bitcoin related sites. But I must confess that the best way to advertise your coin is on this forum by held signature campaign or buying ad space. The major factor to attract investors is how unique your project is, yup it depends on your project, nowadays people are more selective to choosing ICO as their investment, On the other hand, I see some success ICOs which I never saw on btctalk before, I don't know how they promote their ICO.