this setup allows for constant spamming of your spells without running out of mana until using all of your spells twice

janna is strongest with her allies using your ultimate can save a teamate or teamates even if you only you use it for the knockback ALWAYS try to lane with an ad hero (examples:master yi,wukong,ashe,caitlyn,vayne,etc)

as in all supports i strongly recommened you take clairvoyance to spot possible ganks on your allies or yourself which is what a support should be doing with wards or this spell
heal is also good for supports because they tend to get focused in team fights

alternatives to heal:
clarify not as good as heal because some champions dont use mana so it'll be useless for them
flash not really the best spell for supports but if a enemy gets all up in your grill this will get you to a safe distance behind your teamates