There is 2 different playstyle in druid healing:
if you are a Tree, you use regrowth, rejuvenation and lifebloom, you also have Nature's swiftness fo emergency and swiftmend. as a tree I have 3 lifeblooom at the tank all the time and use regrowth if needed, other partymembers get healed by lifebloom and rejuvenation, sometimes regrowth. I use swiftmend when its needed and use nature's swiftness if the tank is going to die in a second or so.I almost never go out of tree form only for cure poison and sometimes when there is not so much healing needed, then I can use some moonfire or so. I can´t use healing touch in tree form and I almost never go out of tree to use it. When you heal in tree form you keep the health high all the time and heal all the time, you are good at healing many people at the same time because of HoT
The other type of healing druid is going down in the balance tree to get dreamstate( its called dreamstate build) You heal in normal form and use mostly diffrent ranks of healing touch, to save mana. regrowth is to mana expensive in normal form, and seldom can be used. You have to let the health at the tank go down a bit so there is enough space for the healing touch you use. I think its good to often use low to middle ranks of healing touch and heal often than wait to use the highest rank of HT.