Flash heal and PW:S are your emergency tools when you need to quickly heal something up, and you shouldn't use these as your bread and butter. Also note that unless you absolutely have to, don't shield rage tanks, as you will rob them from gaining rage from getting hit, and they'll be sad about it.

Renew is solid if it's talented. If not, just stick to using Heal. You can use the downranked versions if your highest rank is too effective for the dungeon in question. When you play without a ton of +healing gear (like at level 39), highest ranks are actually most efficient on mana provided that you don't overheal. Downranking can be reasonable thing to do though if you find yourself constantly overhealing.

And if nothing needs immediate healing, just wand away.