• http://www.worldoflogs.com/reports/omcyj4rtbo300skb/sum/healingDone/?s=9524&e=10144 shows the healing for the Omnitron kill. Take a look at the flow of healing, the spells cast, and adjust as needed. Remember to take a look at the damage taken graph (http://www.worldoflogs.com/reports/omcyj4rtbo300skb/sum/healingTaken/?s=9524&e=10144) as well so you understand the environment.
• Remember AoE heals and fast heals are expensive. You will have to adjust your style of healing. The medium speed cheap heals are more effective; resort to the big, slow, expensive heals for when the tank gets hammered. Use the very fast, very expensive heals to do quick spot healing as needed. AoE heals should only be used when there is a massive amount of damage going to everyone.
• Remember your procs and synergies with spells. For example, you can cast Chain Heal on a Rip Tide target and get an additional healing bonus.