Nik, I've seen you get killed as Naz-Gul fairly quickly, after spawning and getting very small kill streaks. So to help you out, here's some advice:
-Don't go after Lossanarch Axemen!
-Be cautious around spearmen, wizards, and swordsmen.
-Look for archers that are alone and not focused on you!
-When planning to take on a spearman, wizard, or a swordsman, use /scream to blind them. That would give you a moment to get them off guard.
-Take people by surprise, go into the skies high enough so they can't see you but you can see them. It works great with Optifine with the zoom in control/feature.
-Be careful around people that seem AFK, for it is a common trick to act AFK, let a Naz-Gul come close to you, and then surprise the Naz-Gul and kill it. Don't be fooled by those "AFKers"!
-When on low health, get away from the battle and retreat, then look for a lone archer that's not focused on you, and kill him to get regen!
-Grab people instead of hitting them with a sword. You should because more health = more time you can live, use Naz-Gul, and kill people).
-Do not try and grab someone or hit them if they are fighting someone else, even though they may be distracted, since they are in a fight, their sword will be swinging everywhere and can very easily hit you. Even if they don't mean to.
-Don't go after people that are in groups. For example, don't go after an archer with swordsmen that are near by.
-Use your fly ability to get a head start to get to flags. The quicker you can get to the flag, the more likely you are to get there in time to get the 25 points from capturing the flag.
-When going AFK, go to a safe, secluded spot away from the front lines, or go up into the sky really really high!
-Don't get over confident, just because you have Naz-Gul doesn't make you invincible, Naz-Gul is O.P. offensively but very weak defensively!
-If you don't manage to grab someone within 3 or 5 seconds of getting to the ground where they are, fly away, they will use that 5 seconds to gain awareness get ready their weapons, and try to hit you.
-If you try to grab someone, or manage to grab someone, but you can't fly up because the fly key won't work, try running away from the battle, because people will see a down Naz-Gul that can't fly as an easy target.
-Once grabbing someone, get up as high as you can to make sure they can't possibly survive the fall.
-Do not grab someone and go over water because they can land in the water. (This mainly happens on Minas Morgul with Naz-Guls dropping people into the river).
Hope this advice helps you Nik
-Your friend, Legolouie