You can plan strategies on how you spend your mana but there's no rotation for WHM. The most important thing is to keep up the regen, it saves not only PMs but lives as well. Tetra is powerful but takes just a little bit of time to be available again so I tend to keep it as an emergency heal in case something goes wrong. When you mono-heal, Cure is enough most of the time but I heard (didn't read it anywhere though) that Cure II gives a lily everytime, which would make it a better choice as you can cast divine benison pretty much whenever you want. After that, don't hesitate to abuse Assize and Asylum. Asylum is very good paired with other regen abilities (regen, extra medica) and gives you some time to apply your dots. If you want to dps, Holy is good but costs a lot so watch you MP bar and use lucid dream and it'll go up in no time.

tl;dr: keep regen up, heal what needs to be when it happens (or prepare cast when you see it coming), dps when it's calm and keep an eye on you MPs.