Development team- The people behind the ICO will tell a lot about whether or not it is a viable and a potentially successful investment. Look for real people, with real names and do your research on them, especially on LinkedIn or GitHub.
Trawl through Bitcointalk.org- This message board offers insights into the more technical side of things and most ICOs will put up an ANN- announcement board. It allows for potential investors to get some deeper insight into the project and to ask questions directly to the developers.
Read the white paper- The white paper is the point of all information for an upcoming project, it is the promise, and the plan the ICO hopes to take. Make sure you understand it, it makes sense to you, and you believe it.
Diversify- Cryptocurrency investment in itself is a risk, and ICO investment is an even bigger one. Make sure if you are branching into ICO investment that you are not simply backing one horse. Spread out and look for a number of promising projects.
Research- There is so much hype and excitement in the world of ICOs that it is easy to get sucked in without doing the proper legwork. Learn all you can before you shell out any sort of investment.