First things first, avoiding aggro. You avoid aggro by keeping whatever you DO want to attract aggro (typically the warrior(s)) just outside of healing range - that's just a little further than the grey circle around your blip on the radar. Once monsters have stopped running and are wailing on him/them, you're free to get a little closer.
If you stand adjacent to a monster (for instance to cast Symbol of Wrath in your build), the monster gets a choice: that beefy warrior, or that juicy monk. They'll go for the monk. Avoid this by standing -just- a little further away from the monster - the area effect for 'adjacent' is just large enough to allow you to keep a step distance between you and the monster, which avoids the monster switching to you.
Check your health and armour. Through liberal use of superior runes, your health can drop below that of your teammates, and monsters have a knack for sniffing out the weaker guy in the pack - you. If you're still using 51 armour (from Amnoon Oasis), try the Crafter outside of Sanctum Cay (head into Stingray Strand, keep left until you see a Crafter NPC) for 57 armour options - higher armour makes you less attractive.
In a group, point-blank smiting through something like Symbol of Wrath and potentially Zealot's Fire can only work if you have a competent monk there to save you, or if you supply your own healing (and a smiting monk using Orison of Healing and Healing Breeze to keep himself alive will typically not have very much damage output). With you up front, you will be taking the hits, not the warrior(s), so make sure you or your support can handle this.
If you insist on being up front, accept the fact that you will be taking damage, and use it to your advantage. Bring both Essence Bond and Balthazar's Spirit to get 2 energy out of most hits on you (only non-physical, non-elemental damage won't trigger Essence Bond), and use a self-heal like Divine Boon (a maintained enchantment, but for some reason you can keep casting it on yourself with 0s recharge, 1/4s activation and triggering itself, coughing out a decent heal for 7 energy) along to not only keep yourself alive, but send waves of pain every time you do it on top of that. Taking Blessed Signet along can help you recover energy inbetween fights and during longer fights - with Essence Bond, Balthazar's Spirit and Divine Boon up, your natural energy regen can be problematic if you're not getting hit enough (for instance when facing only one enemy). If you have room for it, Divine Spirit (at high divine favor) can help you spam Divine Boon repeatedly in a pinch, which through Zealot's Fire also improves your damaging efficiency considerably (through the nature of Divine Boon, you will be using up 3 energy per cast - if you find this is eating into your energy too much, make sure you cancel the Divine Boon enchantment after every cast, which will reduce the cost to 1 energy per cast - this significantly reduces your self-healing capabilities though).
However, in a group like that it is far more efficient to smite from a distance - remove Symbol of Wrath from your bar, take a Signet of Capture into Riverside Province (or Sanctum Cay), track down the Damned Cleric boss, and capture Draw Conditions from him. Now bring Essence Bond instead of Balthazar's Spirit, cast it on the tank you notice gets targeted the most, and use Balthazar's Aura for brunt damage and Draw Conditions repeatedly on the tank (at 0s recharge and 1/4s casttime, this shouldn't be a problem), triggering Zealot's Fire with each cast. Divine Spirit really shines here - if you can crank it up to 10 seconds or more, you can basically keep mashing the Draw Conditions button which should make quick work of whatever is bugging the tank. The disadvantage of this setup is that you don't always have the option of staying way behind your tank (the cramped quarters of Thirsty River are a good example of this), and it requires a good tank who knows you need him to be hugging the monsters.
Considering your weaponry, try to get an Insightful Holy Staff/Smiting Staff of Enchanting (+5 energy on insightful, +20% longer enchantment duration on the Enchanting part), the former will simply increase your smiting capacity, the latter will tack on a good two or three hits on Balthazar's Aura, lengthen Divine Spirit for precious seconds and make Zealot's Fire less of a pain to recast (although this skill is incredibly forgiving in this regard anyhow). Having 20% chance on fast smiting prayers recharge and 20% chance on fast smiting prayers casting is probably best for this sort of setup.
Finally, take along skills that fit the circumstances. For instance in the case of Thirsty River, Smite Hex is a nice complement to the build. Note that if you're a smiting monk, you shouldn't need to bother with Healing Prayers at all. Max Divine Favor and Smiting Prayers, use double superior runes to push them beyond 12, and rely on the competence of your teammates, or Divine Boon in case you're up front, to stay alive.
