of course a good investor will first do its own research (whitepaper, roadmap and etc), besides that what is your biggest motivation?
Check how hype is the project and how many investors want to invest on the project. You can easily check it on the project telegram group, if many investor chat and talking everyday on the telegram and discuss about the ICO, it means many people want to invest and always invest on presale/private sale, because you can get big bonus.