If Righteous FuryRighteous Fury's duration ends while Kayle is in the middle of her attack animation, she will hit the target, but neither the bonus damage nor the splash will be dealt. The attack is considered ranged.
It is possible to hit enemies easily while staying at the back of your minion wave by using Righteous FuryRighteous Fury. This can be accomplished because not only does the splash damage 'spill' over to nearby enemies when you last hit a minion, but also allows you to harass melee enemies. Staying behind your wave in this fashion will let you wait for cooldowns and heal yourself or allies.
Intervention is also an effective ability to bait enemies to attack or turret dive at low health making them commit to killing your ally or die.
It may not always be best to Intervention an ally when they are nearly dead. If they are about to receive a large amount of burst damage (such as Annie's combo), shielding them will absorb more damage than if you were to shield them just before death (which may end up saving their life or prolonging it more effectively than if you had waited until the last second).
Try to force Kayle to use her spells and then back off, due to her high mana costs in the early game. This way she cannot farm as easily and reach her very potent late game.
Kayle is very weak early game, burst damage can easily kill her.
Kayle can use Intervention to avoid damage, but while in this state she is still vulnerable to CC effects. Use this tactically when she turret dives to have her still take damage when Intervention's short duration wears off. (2 / 2.5 / 3 seconds).