if your having trouble targeting them fast enough, IF you have a mouse with more than 2 buttons then use healbot, takes the targeting process out of it, all you g2 do is click the spell to their bar.
But if its your spell rotation, then its simple : USE WG EVERY TIME ITS AVAILABLE.
When im in Naxx, maly,OS, anything but 3d me and my 2 good healer friends (holy pally and shammy) just fight for top healing since we got nothing else to do. ALl you do to beat them is WG, then give rejuv to targets. If someone is like only 3000 hp down do nourish, if they are way down do rejuv then siwftmend or nourish.
But man you shouldnt have trouble raid healing, you do WG then whatever you want while its down, then do it again.
But as a tip, try not to get used to lifebloom in any form of healing, unless you KNOW they are getting hurt in 9 sec. For after this patch, it seems like using lifebloom as a main heal will be deadly.