Shaman healing is simple. Lets first cover a few spells.
Riptide(RT): Instant heal + HoT. (Bonus effect of: increasing the healing from your next chain heal by 25% but consumes the HoT) heals for about 12k with full duration HoT. No overheals.
Lesser Healing Wave(LHW): 1.5 second heal for 5.5k (6.7k glyphed)
Healing Wave(HW): 2.5 second heal for 13k
Chain Heal(CH): AoE smart heal that jumps from your primary target to the next lowest hp player within 10yards. *Jumps 3 times, 4 glyphed* primary heal hits for 9k--->6k--->3k--->1.5k. Healing Scales with crits. A 15k primary heal lands a 10k on the next person and 6k on next and then 4k on the last.
Earth Shield(ES): Heals the bearer for 4k when direct damage is taken.
Few basic rules and tips:
*Should you want to chain heal a target that was previously targeted with your riptide, do not use it if the HoT has 4 or more seconds on it. you do not want to eat more then the last tick if you are going to do so.
*CH will be your main heal as a shaman, but it is imperative that you continue to toss riptide on (whack-a-mole) sporatic single target damage and ES needs to be maintained on the tank at all times.
*HW should NEVER EVER EVER be used unless it is the first or second spell following a RT or CH. RT/CH will reduce the casting time of your HW by 30% and increases its healing by 20%.
*Always be sure to have Earth Living Weapon(ELW) applied to your weapon. Sounds simple enough, but you have no idea how often i get whispers from pug shamans or guildies saying "LOL, i didnt even have ELW on" Even i've forgot it a few times
you'd be amazed how much healing it does.
*Know that you are a Shaman are you are the best healer of all.