The biggest mistakes developers make that leads to bad ending for many projects are
1. Huge Discounts
Many new projects are still making this mistake over and over again, huge discounts like 50% is insane and it always bother me how the hell the early buyers won't end up dumping since they have already see big profits.
2. Lack Of Solid Products and Ideas
Lack of working products and real use cases is why many investors are not taking new projects very seriously, no one would want to hold such tokens or coins for long, developers need to start working on how their project's token or coin will be very demanding throughout the globe
3. Bad Exchanges
Imagine new projects that make over millions of dollars in ico or ieo and end up listing on bad exchanges with no enough volume, what do they expect to happen?
4). Bounty Payment in Weekly. (Altcoin)
They pay bounty hunters immediately, which is not a good idea as bounty hunters can sell them at cheaper price on decentralized exchange like forkdelta and etherdelta.
5) Not implementing KYC.
Because it could be the entrance to fraud. Many bounty hunters are looking for bigger tokens so they are making way to make more money and one of them is to sign up for multiple accounts.