he's not weak against ganks
keep your passive shield high by poking often to avoid damage from ganks.
you don't have to do anything special with your rune page, an ap rune page that works for most ap champs should suffice, but spell vamp would help though those runes aren't cheap.
first things first, hextech revolver or kage's lucky pick. either or. if you aren't farming well kage's, if you are hextech revolver. if they have a lot of ap think about a spirit visage as it also increases your spell vamp.
you'll want a zohnya's and a liandry's. the liandry's torment will reset with each ult tick so keep that in mine when you place your ult. and don't just ult anyone either. get a priority target. think about where your team is, if you need pushing power, take out the tank with your ult on him so you have this massive meat shield to tank turrets for you. However if you are pushing well or have a tank willing to take turret shots if need be, grab an adc to push that turret faster. Remember the objective isn't kills its pushing.