These are the macros I use for targeting:

1. Set focus to the first non-nead, non-mind-controlled character
/focus [target=aeara,help,nodead]; [target=aebra,help,nodead]; [target=aecra,help,nodead]; [target=aedra,help,nodead]; [target=aeera,help,nodead]

2. Attack either the minion's target or the main's target (same for all damage spells)
/cast [harm,nodead] Lightning Bolt; [target=focustarget] Lightning Bolt

3. Heal either the minion's target, the main's target, or the main (same for all healing spells)
/cast [help,nodead] Lesser Healing Wave(Rank 4); [target=focustarget,help,nodead] Lesser Healing Wave(Rank 4); [target=focus] Lesser Healing Wave(Rank 4)

4. Target the main's target: /target focustarget

5. A set of 4 macros for /target aebra, aecra, aedra, aeera

6. A macro to /cleartarget

Explanation: because of how the game shuffles information between the client and the server, using focustarget rather than an /assist macro is faster and more reliable, especially if you're playing on the opposite coast from the server, at 300-400 ms lag. Most of the time, my minions have no targets, and will attack whoever the main is attacking, and heal the main, via focustarget.

For more complex fights, I can hand out a target for them to burn down in advance, via the target-main's-target macro. Since they now have a target, they will burn this down first, then return to attacking the main's target unless I assign them a new one. I don't end up needing this option much, but it is handy.

When a specific minion pulls aggro or gets hit by some attack, I hit one of my four specific-target macros, and then cast a heal. Because the minions have targets now, the heal will go to that target rather than the main. Once I'm done, I hit the cleartarget macro to reset them to healing the main. If I need to heal a target that I don't have a minion /target macro for, I can target it with my main and either use my target-main's-target macro (for more long-term healing) or just throw out a quick heal thanks to the [target=focustarget,help,nodead] condition in the healing macros.

The important thing here is that 'target' is being used like a 'focus' for the minions. So it's important that the minions' targets be cleared most of the time, which takes a little bit of getting used to. Once you do, it works very smoothly.