most of the ICO's are either scams or projects looking for Venture Capital.

Therefore, the chance of them failing is reasonably high, how high exactly is hard to estimate since they are a very recent phenomenon,
so, things that increase chances of success are:

- a well-designed roadmap that has dead-lines that are actually being delivered (and can be verified) and clear reasons for
- a sensible idea that is achievable (preferably coupled with clear plans to become and remain profitable not involving magic or other investors) and that provides value
- well-known people on the team (since this guarantees better access to more conventional sources of funding for them if necessary)
- preferably also a team that emphasizes informing investors and potential customers