Three things:

1.) Looked at your Lodestone profile and you have no accessories. You'll want to invest in either getting VIT ones (for more health) or STR ones (for more DPS/aggro).

2.) You'll want to go WAR in Brayflox - MRD has it's merits in some dungeons but for the most part that extra boon to HP and access to Inner Beast is a life saver. The increase of healers cure potency on you is actually 20%, which is quite significant. Sometimes you can turn Defiance off to deal more damage, but your first job as a tank is to keep aggro and not die - both of which are helped greatly by having Defiance on.

3.) As Ashkendor said, make sure you're popping defensive CDs, even on trash. It can help a lot. Some relatively experienced healers will DPS, so you may dip lower than normal, but the good ones won't let you die. If you do die, and you've used defensive CDs, it's their fault.