Take advantage of Soulstone/brez
A strategy we've begun to apply is after your first tank clears his initial stacks let him continue to tank Halfus right up until he dies, if SS'd he can instantly rez himself or just be quick to brez him while your second tank takes halfus, this way you aren't stuck with an extremely gimped tank for that 30 seconds which tends to be one of the most healing intensive parts. Saves early mana costs and if your tank can live up until aroun 18 stacks of the debuff before dying you just bought an extra 10-15 seconds of mortal strike being applied to any other tanks. It's really nice to not have any more then 1 tank with the debuff for the first 1:30-2 minutes.
Our tacts for Halfus HC 10m
After reading all of the other guild's tact, I feel obligated to also post out experience in downing Halfus, I won't say it's perfect but it works for us.
Tanks: DK, Druid, Paladin
Healers: Holy priest, 2 Holy paladins
DPS: Arms Warrior, Ele Shaman, SP, Fire Mage
tactics for us was that we released ALL dragons at the start, enabling all debuffs on Halfus (and thus making the fight manageable from a healing perspective). Also: having the stun & scion active makes MS-debuff on tank very doable. On top of that we had the paladin tank Halfus (solemnly), and he could use Divine shield AND BOP on himself. A few mins into the fight I (Holy Paladin) would use BOP again on him. Only after that (well 4 mins into the fight) did we need to switch tank on Halfus. By that time 3 drakes were dead, and we chose only to kill three and zerg halfus. Druid would tank 2 drakes, DK tanks 2 drakes and whelps. You would not want an extra drake on Pally tank, due to casting DS / BOP and losing aggro (one target is very doable).
Note on healing: pop CD's directly, and go ballistic, regen mana after welps & first drake is dead. You might wanna ask for innervate / hymn / totem.
Although we also tried killing 4 drakes, it only took us to 13/14% (a few times). Prio are the welps, then other two drakes are irrelevant as to which you kill.
We also used Heroism in 2nd phase, instead of phase 1. This slows down the killing process, but the killing on halfus in P2 is like almost instant (i know, exaggerating, but VERY fast). Also benefit of Heroism in P2 is having to deal with lesser raid stuns due to Furious Roar. note on that: Human paladins can break that twice: once with divine shield, and once with their racial (although the last one will you get stunned again), and as a pally you can also BOP someone just before (pref a healer or tank). Warriors can use beserker rage (!?!). Mages can blink.
Ow and during the fight we have our Warrior on Halfus as a dedicated interrupter, just to be safe.
All and all a very doable fight for well geared guild!