Guild Wars 2

Hey you guys, never really looked on the forum, but I just wanted to ask around.

So, I just recently hit lv80. Up to around lv60, I could more or less do whatever I wanted and be able to kill everything. However, when I started running dungeons (I was so late to the party there haha) and around when I hit lv80, I started getting my butt kicked. I can get around and do stuff, but among my group of friends (5 including me), I feel like I am the most useless when it comes to fractals and dungeons. I do alright damage, but I die super fast, to the point where I am more of a liability than anything. Any tips on how to do better?

My current build:
lv80 d/p and shortbow thief
25/30/0/15/0

for 6-0, i use:
hide in shadows
shadow refuge
Assassin’s signet (power signet)
signet of shadows (speed signet)
Dagger Storm

I really want to ask now because I am in the process of gathering materials for lv400 leatherworking armor. Or is there another armor I should get?

Thank you for any advice you can give me.