I will start by saying that the key on a nightblades for sustain is siphoning strikes. Also if you have issues with sustain I might try to run one glyph of reduce stamina cost on your jewelry. I might also try to get sprigans thorn set in Bankori as it gives more damage than Leviathan and has another stamina bonus. Ideally I would run sprigans jewelry blue in the beginning with two body pieces and weapons and 3 body pieces hundings rage. I would also run the lover stone.

To really understand how to increase your damage it is helpful to understand why people use the skills they use and when. Most of your increase in damage is going to come from weaving light attacks between skills and only reapplying skills when the damage finishes.

First and foremost, you should really work towards getting Vicious Ophidian. It is an amazing set when it comes to sustaining your resources, 2k stamina when you kill an enemy, 8% reduced stamina cost, as well as a ton of raw stats, nothing can beat it when it comes to solo play. It drops in all the Craglorn trials. Just get in a group in Craglorm via chat and do any of the three in normal difficulty and you should be good. And with the new changes to Night Mother's, it is not a really good set for nightblade anymore. As far as monster set goes, Engine Guardian is not really a good choice for PvE. Try getting Kra'gh from Vet Fungal Grotto I or Velidreth from Cradle of Shadows, if you got the Shadows of the Hist DLC. So to sum it up, you gear should be like this: 5x Hunding's Rage (2x daggers, 3x body pieces), 5x Vicious Ophidian (3x jewerly, 2 body pieces) and then your monster set. For your back bar, run a hunding's rage bow but your goal should be to get a Maelstrom bow, which drops in Vet Maelstrom Arena (you need the Orsinium DLC). For weapon traits, run infused on your main hand with a poison enchant and a sharpened off hand with a disease enchant on it. For your bow, run infused with an increase weapon damage glyph. And of course, all max stamina enchants on body and a divines. If you got undaunted, you can do 6 medium and 1 heavy for some extra health and stamina through the undaunted mettle passive in the undaunted skill line. Make sure your max health is arouns 18-19k. Once you get more experienced, you can drop it a bit to get some extra stamina.

For consumables, you should be running essense of weapons power potions. They give you Major Brutality and Major Savagery, bonuses which will boost your damage signficantly and for buff food, run dubious camoran throne. Also make sure to use the warrior mundus stone.

As far as skills go, your main bar should be: Killer's Blade (very strong execute skill that heals you for a decent amount), Steel Tornado (bread and butter AOE spammable, use it when fighting 3 or more enemies), Surprise Attack (bread and butter single target spammable), Relentless Focus (8% increased damage done, 10% stamina recovery, and a spectral bow after five lights or heavys, very powerful skill), and Resolving Vigor, which is a MUST HAVE. Should take you a few hours to get it in PvP. For your front bar ultimate, run Soul Harvest. 10 ultimate per kill, which means a lot more back bar ultimate usage and the ultimate itself is really cheap, meaning you can use it if you do not have enough ultimate. It does some nice damage and also increases your damage done against the target you used it on by 20% for 6 seconds. Another great option is Rend. Very strong heal, but its hitbox is a bit weird, so be careful when using it. On your back bar, run endless hail and razor caltrops, both are very strong AOE tools which will help you finish packs very efficiently. Then run poison injection, which you will want to use mostly against bosses, since it does some disgusting damage under 50%. It is also your ranged spammable, so when you cannot get near a target, use that. Your last two skills should be Leeching strikes, which provides a decent heal and some stamina return on light and heavy attacks, as well as a burst stamina return which works like the Rally heal, and rearming trap, which gives you a juicy 10% increased critical damage. For your back bar ultimate, you have many options. Dawnbreaker of Smiting, Shooting Star, Ballista, Soul Tether, Bolstering Darkness, e.t.c. Play around with all of them and see what you like.

And finally for CP, on your blue true, run 43 into mighty and then start spreading your points into thaumaturge, master at arms and precise strikes. For red tree, go 10% into hardy and elemental defender and dump the rest into ironclad and for green tree go 43 into mooncalf, and then put most of your remaining points into reduced dodge roll cost, and finally put a few into break free, tenacity and block. Good luck and have fun!