If you are totally new to ICOs I recommend the following guide as a starting point:

https://coinclarity.com/ico-101/

I'm going to be writing my own personal guide to ICO investing, probably a bit lengthier than the one listed above, having followed the phenomena since 2014.

If I had to limit the criteria to 3 things, I would have to make some sweeping, all-encompassing generalizations:

1. What is the ICO attempting to accomplish that no other project before it has? How original is the idea? Is there a sincere reason why this project could be profitable and successful, or is it just a copycat / clone of another, previously successful idea?

2. Do a gut check on the legitimacy of the ICO. What do your instincts tell you about how sincere the ICO team actually is? Is there a whitepaper, a public dev team, a decent website and decent community interaction?

3. Who is backing or supporting this ICO? Does it have any notable investors backing it, preferably ones with a demonstrable success record? Is it just trying to raise funds from an anonymous public or are there any other companies / individuals signing their support for it?

This is just a summation of about 10-15 different things I research before investing in an ICO.