Very well
First of all get this macro:
#showtooltip
/cast Judgement of Light
/startattack
Now, since the OP said he has or will have valanyr, you want your judgement of light on the boss at all times because when valanyr procs, judgement heals also make shields on the raid. Its not priority so dont stop healing just to use judgement. Also the starttatack will make sure that you are always auto attacking the boss, this means that you have to
1- Always stand next to the boss (it is possible in every single ICC boss)
2-Heal the raid with mouse over using some kind of raid frames (Grid2, Healbot, etc)
So what you do is stand next to the boss, target it, hit macro and just heal the raid. With melee haste from shamans or frost dks you will melee the boss a lot this getting lots of mana.
There are moments when you must spam heal non stop because of increased raid damage and that is ok, you should have enough mana before that happens so you can spam without worrying about going oom. The idea is to reduce overhealing as much as possible and it can be done if you are not spaming holy light 100% of the fight, it takes skill but its not impossible.
Now, bad paladins will say "well I can just use divine plea with wings and divine illumination to get mana" but then you would be wasting 2 awsome cooldowns just to get some mana back. The moment you learn how to not use divine plea, you will become 10 times better at hpala.
But not everything is perfect, sometimes you have a bad raid comp, or just bad healers that you have to carry so your mana starts going down, this is when you have to learn to use your cooldowns properly. Use Arcane torrent if you are a blood elf, Divine illumination with meteorite crystal and stuff like that.
Should never use divine plea while healing, only on the downtimes like sindy flying away, LKhc transiton, right before LK sucks everyone into frostmourne and maybe bql moving to the center, but be sure to dispell it when you are going to start healing.
Where to stand as hpala?
Marrowgar: huge melee box you can melee him all the time basically
LadyDW: you can melee here all ph1 and you should have enough mana for ph2 if you dont wanna stand next to here during that ph, but you could still do it, just eb careful when mind control is coming
Gunship: Melee the adds in your ship, put beacon on the jumping tank since it has 60yd range
DBS: you can be next to boss no problem, the only threat would be the first second beasts spawn you might aggro 1 but they will lose aggro once the dps starts killing them
Festergut: stand around tank so you can still get the spore buff, be careful for malleable goo!
Rotface: so easy you can stand next to the boss all fight and bubble when explosion comes if you dont wanna move
PP: Follow the boss around when tank is movng him, just be careful for the choking gas spawns
BPC: this one is a little tricky, I usually go next to keleseth from the begginig so I dont have problems with the vortex. You can try to use judgement on the active boss and then switch back to auto attack keleseth or just dont change targets at all and focus on healing.
BQL: stand at the side of here, almost close to the tanks to avoid the aoe dmg melee dps take, be careful if you are going to use bubble when you get flames because it will spawnn all the flames in same spot and you dont want that close to the tanks, run away a ittle and bubble if you want or just do the normal thing and run along the wall
Sindy: huge melee box just dont go to uch to the back so you dont get tail smashed. You can use divine plea during air phase if needed but you can also just auto attack the tombs. On last phase you should have enough mana to cast without hitting the boss but also you can hit the tombs while hiding, just make sure you are out of Sindys LoS but not the tanks LoS
LK: stand with the melee group behind LK all the time, you move with them for shadow traps and refresh judgement and beacon when Lk is casting his skills, because you know he doesnt attack tank when casting. Use divine illumination and maybe meteorite when LK is around 78% to compensate for the extra dmg. on the tank. If low on mana, use divine plea while on transition and also hit the raging spirits. Ph2 will test your skills a lot. learn when to use wings or divine illumination, always use arcane torrent and follow LK when tank is moving him, sometimes you will have to stand still to spam heals on the tank because soul reaper or whatever and thats when you use your cds so you dont have to use more mana than needed. On last ph, you can use divine plea right before LK starts dragging every1 inside frostmourne since it takes around 4 seconds, just make sure you dispell it after you are inside.
I hope I didnt left anything out. I never stated that mp5 is the devil and that you should avoid it, but getting solace because mana is such a waste when you can have better trinkets that will increase your healing during the raid. Do not underestimate how much mana you cn get off seal of wisdom, everytime it procs you get 4% of your total mana back, at the moment I wrote this post I had 37834k mana unbuffed outside of ICC, my holy light cost is1102 with libram of renewal and glyph of seal of wisdom. Procs from seal of wisdom would give me 1513 mana back, thats more than the cost of holy light already so thats how you get to keep a lot of mana even while spaming heals a lot, also with melee haste buff you will hit the boss a lot faster than the 1.80 attack speed from valanyr. I understand that seal doesnt proc always and that you dont hit boss everytime you cast, but you also have your illumination talent to compensate for the moments you arent hitting anything.
I hope this helps, if you still have questions, PM me ingame Varynnar Horde icecrown. You are more than welcome to keep using solace if you think all I just wrote is poor :P