Do you play a stealthy nightblade, a shooty nightblade, or a stabby nightblade?
Do your most-used skills rely on magicka, stamina, or a mix of both? If it's one of the first two, put almost all your attribute points into that stat. If it's the third, divide them evenly between the two.
Make sure you've got level-appropriate gear.
Don't spend skill points on active skills you never or almost never use. Choose five or seven skills for your rotation, morph them as needed, then put your skill points into passives (and craft skills if you craft).
If you're a stealthy nightblade, you'll be relying on Shadow Cloak quite a bit. This works quite well with Veiled Strike as a main damage-dealer.
Strife is a self-heal. Use it early and often. Teleport strike puts you up close with a mob quickly, so they don't get a chance to wear you down while you close with them. Find a skill that does huge amounts of damage, like Assassin's Blade, Flurry, Uppercut, or Snipe, and hammer on that until you can't anymore.
That's three skills on your ability bar (four if you use stealth). To round it out, add one or more of an AoE (soul shred, whirlwind, arrow spray), a CC (Agony, Sparks, Aspect of Terror), a self-buff (Blur, Haste, Drain Power), an off-beat attack (Summon Shade, Hidden Blade). Adjust these according to what type of enemy you're facing and what kind of group you're with. For example, when I'm soloing a mob I like an AoE and a self-buff. To solo a boss, I'd replace the AoE with an off-beat attack. To go against a large mob with a group, I'd replace the self-buff with crowd control. etc.
Basically, just because you can learn everything doesn't mean you should -- at least, not right away.
"GUIs are tough. Let's go wumpus hunting."