Agreed on learning as much before going in but you wont' know until you try. Thats where the most learning happens.
All that being said, just make sure to check on the healers mana often and have unit frames so you can easily tell if people are dead or low on health. Usually on m+ runs you can chain pull but sometimes you want to give the healer a second of out of combat so they can take a quick sip of water between pulls. Some healers are ok running with 25% mana others want 50% etc. But they definitely don't need to be at 100% IMO. You should be aware of the type of aoe damage packs do, for example the Pelters in Neltharion's Lair or the Scorpions near the end of the instance. If your party is at 25% health and you're at 90% health and you pull the next pack... you're gonna have a bad time.