Read their whitepaper!
Yeah. That simple. You look at how unique their project is and how the community would benefit from it. Then next is the team behind it which is really important if they're legit or not. And you can add a little bit of extra research about it.
You can actially identify each ICOs that are good. By simply looking at the platform itself. When you see that the ICO is really promising based on the platform you should join it. Or even invest on it. Just you are the one who can recognize it.