I know some good sets but pls don't go this way. NB is such a great class, waiting 5 minutes in stealth to gank and 2-shot one guy on a horse is a waste. There are so many other possibilities to try with NB.

Have a 2h as secondary for rally damage bonus, use relentless focus for the 8% damage boost, and reapers mark to reduce armor. The standard tactics.

Also the pvp gear sets like Hawks Eye, Morag Tong and Shadow Walker.

5 pieces of Archer's Mind set with a couple of heavy pieces with 2 piece damage bonus (way of the fire or dreugh king slayer) and some shadow walker jewelry...I was using this combo to hit v12 mobs for 20k+ from stealth with Rally/Relentless Focus/Lethal Arrow. The problem is dps suffers when not stealth because the Archer's Mind bonus is no longer as helpful.

Alternative: After tinkering with my build I was able to get 20k+ from stealth and have better dps out of stealth with 5 Hunding's Rage, 4 Morag Tong, and 2 Shadow Walker.

Depending on level, spec, and whether or not they are aware of being sniped, you can kill a lot of pvp opponents with 3 hits, and occasionally just 2.