I do know that there is no real correct way to believe in yourself, and that it's different for everyone. However, I felt this was the more common, practical and realistic way to believe in yourself, and that other people's methods are kind of just different versions of this way. Press the green flag and use arrows to navigate.
All of this is from my blog at itsagirljourney.blogspot.com. You can find a lot of valuable, motivating information there. I invented and tried the two steps to make me believe in myself, and trust me, it worked. Enjoy! <3 <3 <3