First of all, we clear the two concepts, Stealth and Hidden. 

Stealth —Every class can sneak.  Press Ctrl and enter the sneaking state, which makes enemies at a distance not enable to discover you.

Hidden —Shadow Cloak is ability to disappear for 2.5 seconds. Whatever close distance enemies keep, your character can sneak in the indivisible situation.

Tips: Through actual test, the guild skills are the following:

Magelight: Magelight doesn’t discover the sneaking players, but it can find the players in the situation indivisibility. Thus, when Sorcerer casts the skill, you are able to sneak and attack it.
The common stealth skills: Stealth can be maximized by passive skills.
Races skills
 Stealthy

 Dark Stalker

 

Medium Armor skills

 Improved Sneak

Other Skills (optional)

 Concealed Weapon

Analysis: As to race skills and armor skills, Most of Nightblades will choose to add to the top. The skill Concealed Weapon is capable of increasing the stealth speed by 15%. What is the use of the stealth speed? When a group of monsters rush into you and you just move aside slowly, you feel the importance of the stealth speed.
 

Dark Veil

Dark Veil

When the above passive skills are all chosen, Nightblade cannot be discovered about 8 meters away in the front of enemies.
Intermediate Sneak Skill:
Lots of players complain that even if their passive stealth skills are so advanced, why their characters are found by monsters in the entrances in dungeons so that they don’t directly rush into bosses.

There a nice tip to go through entrances without enemies’ notice in PVP or dungeons.

Shadow Cloak

Every Nightblade knows how to use the skill, but few Nightblades know when to use the skill best.
 
When you come across enemies, you cast Shadow Cloak instantly before the eye icon is open. Passing through the enemies group, cast the sneaking skill in time after Shadow Cloak is over, which keeps eye icon close. Continually use Shadow Cloak across the opponent player group.

I’ve tried to cast the skill frequently in the Beta, which made me pass through the door and ingeniously intrude into the blue castle of the opponent.

The character’s attributes are strengthened in PVP. Shadow Cloak is just used three times. The strengthening stealth speed can assure you can arrive under the stairs of the first layer. I hope you have good luck not to discover by the opponent players when you wait Magicka to restore.

When a large group of enemies rush toward you and you have no time to evade, what are you going to do? (In fact, the situation is very common for Nightblade.)

Strategy: Run to the left side. When the eye icon is half open, cast Shadow Dark. In the views of the opponents, you suddenly appear in their front like shadow and then disappear. They will run forward after the shadow. You succeed in escaped them.

The all above is my ideal about stealth and I hope it is helpful for you who play the Nightblade. Thank for your reading.