Mainly, this depends on your gear/tank's gear and your personal knowledge of the fight. A few other factors that play into your enmity management is how derpy are your DPS.
A favorite opening move of mine is Divine Seal > Regen.
That is usually enough HPS to roughly match the DPS your tank is taking where you can just sit around and watch the fight. Remember to reapply Regen before Divine Seal wears. Depending on the fight, you might not want to recast Regen in cases where adds pop during the boss pulls. This just comes down to experience and knowledge of the fight. Something to note: Do not pop Shroud of Saints as soon as adds pop. Wait for someone else to get on the mob's hatelist, then you can Shroud if you think it's necessary.
