At first varus will be very squishy, but he's an adc so play him like one and use his q to poke the enemy when you can. Don't be greedy, and don't push too hard, towers can wait till later. Farm minions.

When varus gets the second piece of his build, you can start killing for real, and it only gets better as you go. (Note. He still lacks escapes so go for wards) just remember, this build lets you create minion walls and HUGE tower destroying potential. So be careful hiw you use it, as he doesn't stand up well to tanks or ap. focus on minions, and after getting item number 3 you should be able to solo dragon, just remember the blight stacks.

Start isolating empty lanes, and build Up huge minion walls to help hold up any enemy champions. Use chains of corruption as an escape tactic and fall behind minions, then into the jungle. This does not mean you abandon your team, it actually works better with a support to back your movements.

Use chains of corruption to lock down enemy champs while the other members get kills, and try and focus on lowering minion count, or destroying the towers( I recommend the latter), but, know when to run because no one likes a feeder.