Hello,
Healing is one of the most challenging roles in the game, but it also one of the most rewarding. There is no better feeling know that your heals made the difference between success and failure of a boss fight.
This is a quick guide to stats for healers. Sage, Scoundrel and Commando healers do not gear identically, but there is enough overlap that some I can offer some general advice.
Primary Stat: Aim, Cunning or Willpower. Your primary stat contributes to both your healing bonus and your critical chance, so it’s always the best stat. You should try to use all main stat augments as well.
Secondary Stats: Power and Crit. Generally speaking, you can’t go wrong with Power. Power always adds to your bonus healing at a linear rate. Because of diminishing returns, the Crit stat scales poorly in comparison to Power. Since your primary stat also contributes to your critical chance, you don’t need too much Crit. In fact, at higher gear levels you don’t need any at all. Generally, 25% total Force or Tech critical chance is enough; depending on your gear, a couple +Crit pieces are fine.
Tertiary Stats: Alacrity, Surge, and Accuracy. Everyone loves Surge, but how much Alacrity you need is more up to taste. Many guides say stack Surge to 75% then favor Alacrity, other suggest stacking both equally. Many of the sage’s heals are cast or channelled, so alacrity has an obvious benefit, but even Scoundrels with their instant cast heals are helped since it reduces the global cooldown on those abilities making it easier to heal more targets faster. As a sage, I like around 8% (475 or so Alacrity rating), but it’s really a matter of taste. Once you feel like you are able to get enough through put, then go for surge. Accuracy is exclusively a stat for dps, so try to avoid it. This does mean a healer's crowd control abilities might miss every once and while, but that just makes trash pulls more interesting.
In general, different level of stats don’t compete with each other, so that you’ll never have to pick between power and surge on the same mod or enhancement. As Sky mentioned in the Sentinel thread, Mods have different combinations of Main Stat, Endurance and Power/Crit. Unlettered Mods with Power should be your first choice, but “A” mods are a decent second choice. By the way, higher level A Mods are a better choice than lower level unlettered Mods.
Finally, here are some online guides for healers if you’d like to get more in depth information.
Scoundrel: http://www.swtor.com/community/showthread.php?t=56339
Commando: http://www.swtor.com/community/showthread.php?t=635473
Commando: http://www.swtor.com/community/showthread.php?t=641844
Sage: http://www.swtor.com/community/showthread.php?t=708461
The Sage theorycrafting thread I consult: http://www.swtor.com/community/showthread.php?t=647711
