As someone who has been a healer of all classes for a long long time I can tell you that we really appreciate a tank that notices his party, and that waits til everyone is ready to go. This doesn't have to be typed out in a "I need mana" or "are you ready" kinda way. Its easy to tell when a healer is ready. Everyone is at full health and the healer is not sitting down drinking
It's also just a glimpse at the healers mana-bar which takes 0.2 seconds.
In addition knowing your encounter, how hard a certain pack is, will let you know how much mana is needed. but it is the healers job to not slack on drinking, so you can just follow the above tip and you'll always know when your healer is ready.
Another thing that's nice is if your tank notices if you are there before pulling and not round the corner up the stairs with full mana cos that's where you sat down to drink after last fight before everyone else took off
I'd also like to mention that things are certainly different with this expansion and for reference in heroics I like to always be at 100% before a pull cos you never know what might go wrong with the cc / interrupts / silencing and before you know it you have to panic heal and mana becomes very vital
PS) please don't stamina stack