It depends on your play style and what you want to achieve.

There are viable magika Nighblade builds as well as Stamina nightblade builds. There are long range builds with Bows, there are mele builds with dual wield or 2h swords.

There are builds solely for ganking.

There are builds for running in a group.

There is not 1 master build that is the best at everything.

I have multiple weapons and skills that I swap in and out depending on the situation and how I want to play at the moment.

Sure thing,

These tips are for PvP:

For Bow your going to want to get Snipe and Poison Arrow. You can also get Arrow spray for group AOE and morph it into Bombard.

For Dual Wield, your going to want Whirlwind, which you will morph into Steel Tornado (this is for running in a group. AOE)

The rest of the skills I use are class skills. I use Ambush on my dual wield bar, with Dark Cloak and surprise attack. The Fear from Shadow class skills is good too. It morphs into Mass Hysteria.

For your attributes, you'll want to dump everything into Stamina as a lot of those abilities will scale their damage off that.

For gear I would recommend starting with 5 piece hundings rage. Your going to want to stack a good deal of weapon power.