First mistakes started from finding great idea for get millions of invest. People think what great idea can make money.
The first: no great idea. Success startup should sell , improve or help. For example just one page site can sell millions of shirts. Is it a great idea or not?
And why you need million dollars and why you want be gigantic as facebook or google, is it a mandatory?
Other mistakes believe startup standard pattern:
:))))))))))))))))))))))))) Do you believe this will success you?
In the internet millions of startups with this pattern and no one earn 1$ a month.
Why you need investors? My friend have small web project for small shops, and every month he sell 5-10 copy of his product. he just arrive at the shop office install project, run in localhost and return back to home. No any invest needed.
Forget about technologies the first in white paper paint your idea and target!! Forget about global world , millions of dollars!!
Sell your product to one people, one company, one small country!