of course a good investor will first do its own research (whitepaper, roadmap and etc), besides that what is your biggest motivation?
By reading the subject line of this topic, I assumed you are talking about general investments but after reading the open-post, I come to know you ahve narrowed down your question only about ICOs or altcoins. Why it is so ? I mean you people must understand that the investment opportunities from this crypt-world is truly unlimited but many people think it is only ICO way of investment opportunity.
My own factors for choosing a coin/token to consider them to invest are, availability of major exchanges, daily trading volume, all time high prices and current prices. After the recent downfall of whole crypto markets, I make my research based on these criteria and found few coins and I read/started few topics to get opinion from this community. This is my double confirmation way of choosing a right coin. and I always invest for long term holding hence I choose with more care.