I would suggest that you play Ocarina of Time first because it is overall pretty low difficulty and it is very easy to pick up and play. Also the story, characters, and game play are great so you can easily get into the series with it. Another reason being that Ocarina of Time also sets up the basics for every 3D Zelda game afterwords, so you can kind of get a feel of how the games are afterwords by playing Ocarina of Time. Another one I am going to suggest is A Link to the Past (or Triforce of the Gods) because this game took the basics of the original two Legend of Zelda games before it (Legend of Zelda (1987) and Zelda II: The Adventure of Link (1988) and made so much better in my opinion. A Link to the Past is a little difficult though and is very, very frustrating at times so I would hold off on this one until playing an easier game. Other than the difficulty for beginners, Alttp is a fantastic game with awesome game play which is as smooth as silk. The next one I am going to suggest is Link's Awakening which, in my opinion, has the most balanced difficulty of any Zelda game, and overall is an unforgettable experience and an amazing game. The last two I am going to suggest are very similar, these games are Wind Waker and Phantom Hourglass, although these games can be frustratingly easy at times they can be a great joy to play especially PH. Wind Waker and Phantom Hourglass both have Cel-Shaded graphics, which are very lovable and beautiful in their own rite. Anyways they are both very easy to get into and are very fun =D. Well I hoped I helped with your question, and I hope I helped your friend enjoy a Zelda game. So anyways see you later, and happy gaming.