It depends what you're going for. In-game, Zelda's hair ribbons are impossible to accomplish in real life. In order to get that effect, some Zelda cosplayers have added padding inside of the forelocks, covering it up with the wig hair and then tying the ribbons around them. That's if you want to do it exactly as it appears in the game.
If you don't mind taking a realistic approach to the ribbons, just get the forelocks and start wrapping ribbon around and around the hair. For me, I braided the forelocks beforehand, that way I didn't have to worry about my wig hair wiggling around too much. Then I just wrapped pink ribbon around up and down, tying it off in knots. Then I added green ribbon in the same way, up and down. And ta-dah, hair ribbons. The back was a bit trickier, as my wig is really long. In order to get it to the appropriate length, I bundled up the hair and then pretty much proceeded in the same fashion as the forelocks. Due to the bunching up, however, the ribbons didn't come out nearly as clean on the bottom than did the forelocks. However, you won't have to worry too much if your wig isn't as long as mine (mine goes past my bottom >.> ).
Fem!Matsuoka Rin (Free!) - 95%
Grandmaster Robin (Fire Emblem: Awakening) - planning
Kamui (Fire Emblem: Fates) - 29%
Samemi - genderbent Samekichi (Wadanohara and the Great Blue Sea) - planned