What's the best way to find if you are Native American?

My grandmother's father is possibly Native American, as my grandmother has said. Also, she looks vey Native American. I never met him and my grandmother is getting old so she doesn't remember everyhting. My grandfather gave me everything that she had ( aka his name and birthplace.) I've checked the Dos roll and im pretty sure hes not on it, but I was wondering if there is anything else I can do to prove he's Native American. Answers are greatly appreciated.