Cast on Target of Target

[EaMett]

Don't macros your main combat GCDs, they're laggy and will make your gameplay worse

This is absolutely correct and can't be emphasized enough. DO NOT use macros on your main combat skills. Macros do not queue so you should expect a significant dps loss (proportional to how bad your ping is).

This is less of an issue for healing spells since you don't heal that often in FFXIV, and when you do heal you rarely cast multiple healing skills in a row. So it's ok to macro your main healing skills.

In other words: healing the target of the target while targeting the boss is an acceptable way of healing the tank, dpsing the target of the target while targeting the tank is an unacceptable way of dpsing the boss.

Also, because there's a lot of bad advice here. Never create multi-target macros. If one line fails it does not stop the rest from executing and this is another big flaw that has major drawbacks. Consider this macro:

/Micon "Aero"
/aerror Off
/ac "Aero" <t>
/ac "Aero" <tt>

If your target is the monster, that means you want to Aero <t>. But if you press the macro while still on your gcd it's possible that all but the last line fail (because the last line will execute after your gcd is available) so the game will try to Aero <tt> (your tank most likely) and fail and you will need to press it again. Add this to the fact that macros don't queue and you're essentially doubling the effect of your ping.
This is even worse when making macros for heals as you may just end up casting a heal on yourself. Which will set you back the entire cast time and MP and still not heal the person you were aiming for.

The rules for good macros is to:

1) Never macro your main dps skills
2) Always stick to single target macros.
3) Consider the above when making multi action macros.

Edit: I spent a lot of time looking into this when I started. Set my skills up so that all my target based healing skills became mouseover macros. There are some issues with double weaving sometimes but that's about it (it's also in part because my ping isn't the best)