Tradition, heritage, and change all matter to a race. No two Night Elves are the same, just like no two Dwarves or Humans are the same. One should realize that Night Elves do have sub-factions within their society, just like we do today, consisting of the traditionalists, the liberals and those in between.
The key to roleplaying a Night Elf is, no matter what 'side' or outlook you choose, your character is a Night Elf and not a Human or Dwarf. They were raised in a culture much different than those other races and even if they're open minded, their roots still show.
For the sake of this section, imagine a scale going from 1 to 10, with 1 being extremely liberal and 10 being hardcore traditional.
Traditional Night Elves are those who cling to the old ways, the ways before the Third War and the rules and lifestyles of the Long Vigil. These elves very much so embody what it meant to be a Night Elf not even 15 years prior to the current timeline.
Those who are on the far end of the tradition scale will usually and religiously push for how things were prior to the Third War. They may dislike the changes to the Night Elf government and lifestyle, may dislike outlanders or believe that their old ways are superior. As they move closer to the middle of the scale, traditional elves mellow a bit and make concessions or compromises in their beliefs, perhaps still favoring the old ways but able to cope with the new, or approving of some of the gender changes, yet not the inclusion of foreign races. It is, of course, up to you where they fall on the traditional scale, but the higher up they are on it, the more set in the old ways they'll be.
It should also be noted that Night Elves are slow to change . Because of this, it is very likely that the majority of Night Elf society falls in this range, not yet transitioned into the new ways and ties made since the Third War.
An example: A traditional Night Elf will choose a bow over a gun at every opportunity, even if the gun is slightly better.
Adventurous Night Elves are those who are not quite liberal, yet not quite traditional. Here Night Elves may be getting used to outsiders, forming more bonds with non-Night Elves and traveling outside of Kalimdor and Night Elf territory. These elves are far more likely to break with tradition but may still lean one way or another, with traditional-leaning elves still holding on to what they've learned for hundreds of years.
The traditional-leaning may speak up or hesitate to break taboos or try new things, while liberal-leaning ones may be more inclined to experiment. They may understand another race's viewpoints or plight, possibly mixing it with their own ways. They may be eager to understand yet awkward or out of place in another race's city or territory.
Example: An adventurous Night Elf will choose either rifle or bow and will choose whichever suits the situation or is in the best condition, though may still have a bias.
Liberal Night Elves are those who have broken away from tradition. These elves have embraced the new allies, techniques and lifestyles put forward to them. They may be very willing to surround themselves with other races, use new technology and break with heritage. They may feel just as at home in Stormwind as they do in Darnassus, though as said above, roots still show.
Those who join the Argent Dawn, go on away missions for the Cenarion Circle or become mercenaries may be this kind of elf, willing to be near those so very different than their old lives. On the flip side, those who fall into thieving or cults also fall into this range, by letting the new world overwhelm them.
At this point, though, it should be remembered that Night Elves are still Night Elves. Even though liberal, they might prefer their traditional food or prefer the feel of grass on their feet. They'd still worship Elune, given the proof of her existence, but may be willing to accept the Light as a valid view on how to live one's life or even compare teachings and see which is better.
Example: A liberal Night Elf may become fascinated by firearms and will choose them over bows if presented the choice.