Good question. I have several stages before making a decision.
Let's say, I browse an ICO calendar and go through projects one by one.
First impression
1. Website (design, style, template or custom)
2. What is the idea in a nutshell
3. Projects's social links (number of members, real or fake)
4. Team and advisors (if Vitalik is not on board:)
Deeper insight
1. Whitepaper
2. Where company is registered
3. Team's Linkedin profiles and past experience
4. Social activity, interviews and overall communication style
5. Token model
6. Advisors involvement into the project (are they just faces or their input is substantial)
7. Development plan, target market
8. Reviews on rating agencies if available
These are some of the things we have to assume and more we have to check with their advisory team and we have to check whether they attend any public meeting. This another way of marketing their product to which it will boost their activity.