Healing is all about practice and fight knowledge. If you know the fight as far as when damage will go out and to whom then you can better prioritize who needs the heals and when you have time to noble sacrifice to mange your force. This means a dps could be at 50% hp, but you might be able to focus heals on the tank and wait for rejuv to come off cooldown and throw it on the dps and go back to the tank. Or maybe a rejuv then force barrier on a tank gives you a window to then healing trance a dps and rejuv dps and then go back to tank, etc.
Rejuv should be cast before any heal if at all possible so you have the conveyance buff. Even if everyone is full health throw rejuv on someone (tank if the armor buff from rejuv has worn off or yourself if you need to noble sacrifice) to have the buff in preparation for your next heal. I only cast salvation with a 3 stack of resplendence if it's needed right away or while moving. Reason being is because the base global cool down (GCD) on an instant cast is 1.5 seconds. When I cast with 2 stacks the cast time is .6 seconds and with 1 stack it's 1.3 seconds, which basically allows me to start casting another heal or an instant right when it finishes. I have to wait the longest amount of time to cast another ability after casting an instant salvation. So if I have a 3 stack of resplendence I probably noble sacrifice once and then cast it.
There are so many nuances to healing that it's difficult to completely explain how to go about it. The best way is to get as much experience as possible and ask specific questions about things you don't understand or want to know more about.
You can go to my twitch page to see some of our recent raid fights as I have created highlights for each kill.