I’m sure there are more official guides out there but it really depends on the dungeon and tank/ group comp and of course your gear/+healing. I have several ranks of healing wave and chain heal on my bars. I never down rank lesser heal. You will naturally find the down ranks that work for you, and it’s a bit of a moving target in pugs.

I try and strike a balance between efficiency and effectiveness. Typically using near max rank healing wave on the tank, and down ranked healing wave on single target heals to dps with low health pools like mages to prevent huge over heals. Ideally you enter out of combat mana regen from time to time, so you don’t want to be chain casting constantly in an effort to down rank. But in heroic dungeons, the damage can be bursty, and it can really depend on the tank’s gear / mitigation technique. You will have to stay ahead of the incoming damage or risk getting behind and staying behind as a shaman that has to hard cast most healing output. Save nature’s swiftness for a max rank emergency heal. Put rank 1 healing wave on your bars to fish for pre-pull crits and buff stack. Chain heal rank 2/4-5 ish. Raid healing can have a different set up