Different tribes have different standards.
To be Cherokee, you just have to have a Cherokee ancestor.
http://www.cherokee.org/Portals/0/Documents/2012/8/31660Application_Instructions.pdf
If you just wanted to know what it takes to be, colloquially, an "Indian," then you will not get an answer because there isn't one.
You can practice a tribal culture, you can have indian ancestors, etc. There are many ways to consider yourself indian.
If I were to ask you how you know if someone is German, you would say it's where they and their parents, and parent's parents, etc were born, where they grew up, etc.
But what if your mom was german and your dad was japanese and you spent half the year every year of your life in both countries? Then what are you? Are you exclusively one or the other?
What if your ancestors were forced to move all over the place and mix with other cultures?