I play D/P thief but never feel squishy or die. I stay away when I can, hit with black powder and heart seeker to close in, this grants me stealth. I then hit with a backstab, get in about 5-10 hits before they hit, dodge back, rinse and repeat and I rarely get hit. I also put up Basilisk venom when I can. If I'm against a group of 10 or so I'll switch to my short bow and hit with cluster bomb. While I'm doing all this I keep my eye out on my party to see what % their health is on, how long I'll think they will last, if I think they need help I'll drop Shadow Refuge on them or I will Shadow step over to them, drop a black powder switch to Shortbow, cast clusterbomb on the black powder to combo out a AOE stealth. If you try and play Thief as a warrior and stay up close you're going to have a bad time. Keep moving, never stop, a Thief survives on mobility and stealth. Since you're using D/D, don't keep spammning Cloak and dagger, seriously it's a waste of initiative, keep a look at your boons and such and never cast Cloak and Dagger when you have revealed up. during this time use your auto attack combo, Heartseeker is best used for travelling small distances or when you think he is about to die or for combos. If you use steal the second you use Heartseeker you use both and Heartseeker will still hit. Try and use Death Blossom to dodge if you can't use your normal dodge. For instance if you heart seeker and end up in front of the enemy, use death blossom to jump behind him. Cloak and dagger to get stealth and then backstab and jump back. Dancing dagger is best used just for chasing down your enemy otherwise it's a initiative waste. When picking your skills try and pick ones which allow you to either stealth. Get away or put down the enemy. Focus on abilities to keep yourself up and not your party. Take my words with a grain of salt however. I've only been playing my thief for 120 hours and only hit 80 4 days ago. Good luck!