Everyone has had a lot of good points to help. Here are my two cents. Everyone has hit on CC so im not even going to go there
1. Just because you had 2 healers does not make you invincible. It means you werent doing enough damage. With that group you cant take too many pulls, you cant kill the mobs fast enough.
2. Make sure you know your class well. Read up, i have, make sure you have a good rotation and have as many buffs activated as possible. Many of your ablilites give you some type of DR. I play as a guardian and this is a biggy.
3. Always, always, always use your interupts. Above the picture of your targeted mob there will be a little bar that pops up when there is an attack you can interupt, do it. This saves you from a ton of damage, and can be the key to not having a wipe.
I'm sorry if you already know this, but even if it isnt new info someone may find it helpful. Hope you can have some fun with this great game, grouping is my favorite thing aout it right now.