Very good question. What I always look in the ICOs:
1)The idea. Is it new or is it old? Coins that only promise a standard - blockchain, masternodes, wallets, plastic cards, etc., but nothing new, I try to avoid.
2) Always read the whitepaper. It has more details about the project and you can see how well the team is working with documentation. If it's only 2 pages long, I try to avoid it.
3) The roadmap is very important. It has to be reasonable. If it promises too much in very short terms, I try to avoid it.
4) The ways to contact the team. The more means to reach out to the developers, the better the coin will be.
5) Budget. Some coins actually list their budgets - how much % goes to what needs. If there is no marketing budget in that, I avoid it. No marketing - no coin.
6) If the team provides information on how many funds they have raised so far, it is also a good sign. The more investors they have, the more likely to succeed they are.

There is always intuition, listen to your subconscious side. If you don't feel like it is a good idea or have some doubts about an ICO, don't invest. If you have a good feeling about the ICO, the idea sounds good, the roadmap is reasonable, the team is friendly, you will probably be happy with your investment.