Come up with an idea, think it through and make sure that your project actually needs an ICO
If you want your project to be successful, it has to offer a solution that the market currently needs, and this solution should be objectively better than what your competitors have to offer. To achieve that, you need to have a thorough understanding of that market, know your target audience and, most importantly, know what they will be willing to give you their money for.
Obviously, if your project is sourcing its funding through an ICO campaign, it will have its own token. According to the CoinMarketCap's data, there currently are over 1,500 cryptocurrencies in existence. So, if your token is to survive this competition, let alone gain any value, it will need to be in very high demand. To achieve that, you need to think of a way to integrate a cryptocurrency into your project in a useful and meaningful way, so that it becomes an essential and integral part of the product.