Runes: Aery, Manaflow, Absolute focus, Scorth (Or gathering) Font of life, Revitalize
Build: Depends, start with spelltheifs and pots, go into Athens then either redemption or ardent sensor. Don't buy boots unless you have money to burn and you want to drop 1100 on Ionian boots.
Playstyle: Early game you don't want to be attached to your adc the whole time. You actually want to detach to use your passive every time its off cooldown and harass with autos, then when they turn back to attack you jump on your adc to avoid damage and throw a Q. Save your E for when your adc is below 50% during fights.
Team Fighting: Depending on how the fight starts you want to play differently. Your Q is good for catching people out of position and also for peeling. Your ult is also best used as peel for your adc but you could always jump on your tank and try to root the whole enemy team. Jump from champ to champ healing the lowest but always end up back with your adc to give them the damage bonus of your W + Ardent
Levelling: I like to start E for jungler leash, then get Q. Max R>Q>E>W