This should be posted in the Assassin's Forum.
Skills to use:
Lead Attack
Off-Hand Attack
Dual Attack
Off-Hand Attack/Dual Attack
Defense/Healing
Healing
Teleport Away
Rez Signet/Hard Rez
The most important skill you must have is intelligence. You must know who to attack, when and when to runaway.
When I created my Assassin, I had another of my characters find a set of daggers that had +15% damage when enchanted. So I created an A/Mo (who else has long lasting enchantments?). Eventually I had skills that utilized hexes and I found daggers that did +15% damage on hexed foes. So I switched to A/Ne (who else has life giving hexes?). I wanted to make sure I also had a way to get rid of conditions. Eventually I purchased the Signet of Malice. My hexes were long enough, my enchantments were long enough and I had a condition remover. So I then decided to change again for A/W. Balanced Stance and Wild Blow work great (no kds, critical hits, no fear of stances, blocking or evades).
There is no way for a melee character with the armor of a ranger and no defenses whatso ever can ever expect to be immune to death. As you know, death is inevitable (as in real life - the only absolutes are death and taxes; thankfully, in GW, we have no taxes

)
Skills can be segregated into 3 types:
Fast recharge
Good damage
Condition
While you won't find all three in a single skill, some have 2 of the three.
Unsuspecting Strike is a good Lead Attack
In the early stages, Fox Fangs is a good second attack (can't be blocked or evaded). Twisted Fangs is basically a must (good damage, bleeding and deep wounds).
Teleport away is good with Recall or Return (or Aura of Displacement (e))
Teleporting in without a way out is a spelling of trouble. Get in, do your damage and get out. My rule is once you are hit, leave as fast as you can.
I only die because of my stupidity or because I get spiked (or group wants to resign; or no one keeps NPCs alive).
Healing - sadly its either Shadow Refuge or Way of Perfection (you should take Critical eye and Critical Strike if you use this one). Heart of Shadow is okay, but teleporting near another enemy is not good.
Watchout for Blinding from Rangers (throw dirt). Evades and blocking can be countered by Wild Blow, a lucky Wild Strike, Way of the Fox, and Expose Defenses. Using WotF and ED, Wild Strike can remove a stance, which would allow all other attacks to be able to hit. Since its hard to get that 1st hit once a defense is up, use WotF or ED first, then lead with your unblockable/unevadable chain.
As a Monk and a Ritualist, I don't care if an Assassin dies, as long as they do their best, I'm happy. If they aggro insainely, then I get annoyed. As a Necromancer, I love silly Assassins (not stupid ones), as they try to kill, then they die. I use their bodies as a well or as a minion.
As a Warrior and a Ranger, Assassins can do wonders, but they must stay out of harms way.
And as an Assassin, I know from the other professions, that running away is preferable than to stand there and die. Never tank, never stay in the fray more than necessary and make sure that you can escape danger.
Hope this helps you.
Good luck.
P.S. Watchout for Death Novas and Afflicted's own version of DN. Theirs cannot be removed (I've tried in various ways, didn't work

)