It's really about Mana Management and hoping your DPS and Tank are on the same page - With a good tank I can keep him up through most trash with Stoneskin + Regen. In fact you should almost always have Regen ticking on the tank as it heals more over time than Cure spam will. If you feel a bit overwhelmed with the damage the tank is taking or you have DPS that want to choose their own target you can always pick a mob not targeted by the Tank and Fluid Aura + Repose. You also have to keep in mind that many tanks and DPS still suffer from WoW-Mentality where they believe they can rush in pick up everything in 2 seconds and AoE it down. However there are many of both types who will also listen to their healer and will try to work with you...after all it does pay to be nice to the person playing whack-a-mole with your health bar. But in terms of actual assistance with basic healing - Always keep Regen up, and make sure the tank has Stoneskin before each pull.