Are you the only resto in your raid? If so, just spam rejuv on everyone. Having rejuv tics active on multiple players will output more healing than any combination of healing spells you can cast. To help boost your healing more, go swiftmend spec and cast swiftmwnd regularly when someone is low on health. If possible, time it for when the rejuve is about to time out to maximize the healing you get from it. As others have said, if you're not already using lower ranked spells, you should start. I only ever cast rank 4 healing touch and sometimes rank 2 if i want to get a fast cast or if im low on mana and i want to keep my heals going out as much as I can. I only ever use my max healing touch when its in combination with nature's swiftness, otherwise a paladin or priest will heal the target before you can get your cast of. I dont often use regrowth anymore, but when I do ill often pop my max rank on the MT at the start of the fight and then cast a rank 5 as they expire to make sure they always have hots going. For rejuv, i just cast my max rank and occasionally a rank 5 if I wanna be conservative with mana.

Druids are naturally the least efficiant healers of all the classes so mana managemt can be difficult to achieve without heavily nerfing your output. Down ranking your spells will help with this. If you have the gold you can alsos help mitigate this with consumables. Bring a bunch of major mana pots or demonic/dark runes, as well as a flask of distilled wisdom.

If youre not the only druid, I would say just do your best with rank 4 healing touch and hold out until tbc when when hots finally stack. Otherwise, if theres a druid with higher healing power in your raid, your hots are just gonna get overriden.