Go to Tamriel Foundry forums and you can find about 4 approaches for decent NB trial DPS ranging from Funnel to destro to DW. DW probably is the top in NB DPS right now but it is a sucky way to play a NB. Also no one is actually getting 2K single target dps on any important bosses and 0.8-1.2K is just great on non daedra bosses no mater what anyone says. You can of course get really nice number pics on the Mage by sapping the hell out of the axes and popping veils but you should do that one only if the tank messed up and the axes are out of control just like the dks that show they 2k dps on that boss.For aoe dps the sky is the limit for NB but it isn't that important.

All good dps will involve some kind of light or heavy attack weaving though so if you do not do that and do it good , you are not going to get any decent results.

Don't believe too much about those extr high dps numbers they are often very short or special cases. My dps is 4k! And it's 600. It's everything between those two numbers. (The 4k was somewhere in some dungeon when AoE killing tens of weak spiders with Veil and Sap Essence)

I also recommend what @PBpsy‌ said, pick a build from Foundry. Then there are some steps you need to take. It's hard to see how experienced player you are. If you just started, just ignore all this elitist crap for awhile. Much of the dps game comes when approaching max level. Have fun but work with your class and weapon skills from day one. At VR1 or 2 you should have nearly all class skills and passives opened, all armors and two weapons maxed.

Select a "path" that matches your build. You have currently some standard paths to choose.
- Spell crit, spell damage. This uses usually Funnel Health and Sap Essence class skills. Scales with magicka. Good dps and heals while does damage - a survivor.
- Spell crit, weapon damage. This uses Crushing Shock and Elemental Ring. Scales mostly with magicka. High damage but keep resto staff as swap for heals. The weapon damage soft cap is much higher than spell damage cap.
- Weapon crit, weapon damage. This uses weapon abilities from your weapon of choice. Scales with stamina. Very interesting choice after 1.5. Both weapon damage and crit should be pushable higher than spell damage and crit. There is potential for very high dps, but this i still work in progress. Watch survivability, especially if melee.
Below i use the first path as an example, assuming VR14 toon in PvE.

The build works when you maximize the stats it needs. E.g. Funnel Health gives dps only if you maximized spell crit, spell damage and mana. Bow Snipe needs weapon crit, weapon damage and stamina. You cannot make a good NB doing both Funnel and Snipe. Trying to balance and put something to stamina only makes Funnel weak. My message is: go boldly and minmax - it is the key thing to high dps.

As a nightblade you may take Siphoning Attacks with all of those paths. Decision affects very much your gear. If using, you need to compensate the damage loss. If not using, make sure you have resource regeneration plan. SA is unique skill to NBs. It's somewhat less dps but it makes dps perpetual. This is very much sought after in the latest end game content. With SA you can use e.g. Torug's Pact armor, but without you may need Seducer's mana regen and cost reduction.

Depending on your path, make a build and gear selection that maximizes the crit, damage and pool. Only thing you need to balance is health. I am playing today Funnel build and have now 50% spell crit, 127 spell damage, 2650 mana, 1200 stam and 2800 health (with buff food, and yes, i am a bit wimpy and want that HP). How much health you need is personal question. If you seldom die, take 100 HP and move the attributes to your maxed stat. A big part of dps comes from this - have just enough health. Try it! respeccing attributes cost 3k gold.

Select your single target rotation. NBs can make this very simple. It can be as easy as just spamming Funnel Health or Snipe. Make sure you learn to weave light or heavy attacks. Next, make sure you learn your resource management. With the simplest rotation you may get anything between 300 and 800 dps. Find a place to test it and use some addon to measure it. If you use Siphoning Attacks, get used to it's resource returns. Be prepared to fill the randomness with occasional pot. Maximizing the resource pool also increases the return from SA, so push the pool up.

Use Veil of Blades. Currently NBs are most welcomed to groups because of their damage plus their damage mitigation from Veil. Learn to build up ulti. Then, if your base rotation damage is say, 700, drop the Veil and there's your 1k dps. Learn to communicate about veil. It's red and coplayers may jump out of it, and even if they know it, it is a bit hard to see.

Check the class passives. E.g. adding an assassin ability to bar increases crit if you have the passive. Transfer with Sap Essence builds Veil up like no other.

Learn execute phase. When boss drops to 25%, switch to Impale spamming. That alone should make about 1k dps. Learn to both weave it and block and spam it. In AA the mage ends to dps race, and everybody expects NBs to deal with it. Agree Veil rotation with fellow NBs, stack up, take spell power potion, drop Veil when it's your turn and spam Impale. Watch the dps meter. Also, turning off SA at the right moment is like cranking in a turbo boost for the last percents on a boss. When everybody else have empty pools, you go zing-zing-zing. Nothing in this game feels better than that. You are allowed a mad grin now...