The night elves are probably the most difficult race to roleplay well in all the World of Warcraft, which is particularly ironic considering how very popular they are. Many a roleplayer has been disappointed by seeing player character night elves who are 21 years old, who were born in Darnassus or Teldrassil, or whose mother or father is human -- all of which would be next to impossible according to the actual lore of the game. The only way to make things like this is to change the lore to suit your own preferences, or to rely on cliche devices such as time travel and special magics which really go too far into the realm of the abominably self-centered Mary Sue.
Night elves can also be difficult to understand, and full of contradictions: they can be over 10,000 years old, and yet they often do not possess the vast wisdom that would seem to come with such an age; they are deeply connected to nature, and yet they sometimes act without the blessings of nature; their women are supposed to be very fierce warriors, and yet their animation in the game has them bouncing up and down like teenage girls at their favorite boy-band concert.
And yet much of this is just the sort of thing that draws people to the night elves. There's a youthful passion combined with ancient grace and sadness that many roleplayers just love to get into. Also, for those who love to develop long and complex background stories for their characters, there is a great deal of history about the night elves' ancient past which can serve as good inspiration for many of your own character's life events. We won't go into every detail of ancient history today, however; instead we'll cover the basics that you'll need to know in order to start out with a night elf that fits in the Warcraft story, and direct you to some more resources if you'd like to make one with a really deep and complicated background.