Its a good question. I have my own tips for success ICO, project should be simple for understanding, team and advisors must have KYC, milestones should be done at time, by the way bounty and airdrops means not so much for me.
Bounty campaigns and airdrops are just means of disseminating information on the project and creating more awareness. Some investors may not get to know about the project if enough marketing is not done and one of such ways is through bounty and airdrop.