Scepter Discard (sample Disrupting Scepter) I play a permanent that can activate each turn, usually involving a mana cost, to do one of the above effects
Another strategy that mono-white loves to employ is life gain, and Voice of the Blessed is all about life gain
When you do, if you control a red permanent other than Ajani, he deals damage equal to the number of creatures you control to any target
Double strike with prowess is something not every creature can survive, and you should always have combat tricks and spells that give some form of evasion at hand to make this a serious finisher card
This seasons Standard decks probably arent the best indicators of required counts as the mana is so absurdly good, but looking back in time, you probably want 9-11 sources for a splash of a couple key effects and fifteen+ for a solid commitment