Anything can be a scam nowadays. When it comes to ICO's, it's really how much effort you put into research. My process includes reading the whitepaper, look at the the founders/advisors (this is the most important step), and the obvious: how good the concept is. The last part might require some intuition of the market, but is pretty fair to spot when others are talking about it (so join groups and ask questions).
A good example of a successful ICO was civic. All you had to do was look at who started it: Vinny. And then from there, you have a good idea of the odds.
With more current ICO's happening, I read about UnikoinGold and that one's really interesting. Read into the founder Rahul and the people backing and advising. Ashton Kutcher's venture fund and Mark Cuban are into it. One of the co-founders of Ethereum is an advisor and they're close with Jaxx. Also, the concept is pretty rock-solid. For me, this is a great indicator of a successful ICO.
And since I'm preaching out always reading the whitepaper, here's there:
https://static.unikrn.com/4242/unikrn_bm/doc/whitepaper_en.pdf