1) I think we're getting some kind of feathery headpiece - you can always check such things if you check the achievments in game; you can even filter them for achievments that grant specific rewards (like mounts, pets, titles, other stuff).

2) Ideally you want to use it before big raid wides - in casual content it doesnt really matter, though. You have to keep in mind that a healing spell has to trigger it, so either your healers need to pay attention, you need to use clemency on yourself or you have to be in your casting phase to trigger it yourself (since Holy Spirit etc. heals you). The most effienct way is to have it line up with your casting phase so that you can trigger it yourself without wasting a specific cast for it.