Just as with a traditional startup, an ICO's success largely depends on the team behind it. A good ICO team should consist of members with a track record in business, blockchain technology, and relevant industries.
ICOs should have a clear business model that solves a real-world problem. ICOs that lack a concrete business model or only offer vague promises are a big red flag. It's also good to check sites like https://www.gpucoin.net to see if there aren't already tokens in the market that solve that same problem.
The whitepaper is the ICO's business plan, and it should be comprehensive, clear, and professional. It should detail the problem, the proposed solution, and the token's role in that solution.
ICOs that promise high returns with little risk are often too good to be true. As with any investment, there is always a degree of risk involved, and it's best to avoid businesses that aren't honest about that.
Last but not least, an ICO must be compliant with relevant laws and regulations. Non-compliant ICOs pose significant legal and financial risks to investors. And a lack of compliance may mean that the team is not planning to stick around for the long run.