In exchange for his one shots late game, AP varus struggles in the early game. I recommend poking with your Q and trying to use the ult into w empowered q combo when they're low. If the enemy laner is passive, don't even try to play aggressive, if you can just farm and minimize your deaths you'll be able to outscale them.

AP varus in the mid game has a respectable damage output with his burst combo, but it isn't enough to one shot. Hold on to your combo until the enemy is low enough to get the burst. Try to weave in Q's while csing to poke. Roaming can work if you somehow manage to push the wave, but it isn't recomended. Try not to exceed more than 4 deaths to the enemy laner, as they may be able to out snowball your scaling. One shots really start to get prevalent once you get your mythic, boots, and alternater. As for Hybrid, you have a consistent damage output with your poke so just focus on whittling away at the enemy hp bars.

This is where AP Varus shines, your combo can one shot pretty much anyone provided you didn't feed too hard early game. Play around your ult cooldown if you didn't build nashor's and try to get picks and max your ulti hunter. If you run Hyrbid, focus on poking and ulting in when the enemy has about 2/3s hp left, remember, your W active and passive scales of missing health and max hp respectively.