Healing addon recommendations for a noob?

I have been playing WoW since the year it launched and I have never mained a healer. I am gonna try out an orc resto shammy this time around. :D

Can anyone recommend any interface addons that can help me? My biggest problem is that I can never tell who to heal. Moreover, when I can see people with low health in the raid or party, I can never figure out where they are standing so that I can get in range. Is there an addon that makes small health bars that are nice and easy to see? I don't want to see NPC health bars. Also I don't want my screen totally filled with health bars, making my WoW look like a game of 3D tetris.

Any other recommended "must have" addons would be appreciated.