First things first, start W. Try to get level 2 first while also autoing the enemy toplaner to get the three stacks. As you get level 2 immediatly hit your enemy with empowered Q(remember you already have stacks on him from level 1 auto). This way you create an early advantage by getting a kill or burning enemy flash or/and tp. After that simply poke your enemy with 2 or 3 autos(PTA prock) followed by either an E or Q.
After you get level 6 you have a big kill threat all the time and even if you are behind you can punish your enemy for their mistakes and kill them.
If you rush Rageblade, auto 4 times the minions in order to fully stack it and then pick a fight with your enemy toplaner.
Also don t forget to enter the bush to get rid of minion aggro any time you can as you can easily lose the fight because of minion damage.
Varus passive gives him attack speed so make sure that you have it activated when you choose to fight the enemy toplaner. Also don t forget about bone plating as some champions can easily burst you if bone plating is on cooldown.

Varus has no mobility so you can easily die to ganks. Don t forget to ward properly and always pay attention to the map to see where the enemy jungle is situated. If you are safe from a possible gank you can poke your enemy when your wave crashes the tower but be aware of turret aggro. From my experience, you can get out of ganks simply by using ghost(if this is of course one of the spells you chose). You can also use your ultimate to root your opponent and get away. There are some situations where you are ahead and you can 1v2 so trust yourself, stand your grand and pick the target you think you can kill easier. Then, because of the Varus passive, you become a lot stronger fighting the second opponent.

Varus has some serious counters. This ussualy consists of champions that have good mobility and can easily close the gap between you and the opponent. Also a lot of tanks (it also depends on their build and yours) have sufficient damage to kill you so build smart and take into the account your enemy s build and choose the best out of the 3 build options I presented above. Against no mobility champions, ghost is extremely helpful(if used properly, the enemy champions can t touch you). Also in extreme casese, for example against champions like nasus, you can take cleanse.

Varus is extremely useful in teamfights thanks to his ultimate which can root multiple enemy champions. So after the laning phase just group with your team in order to secure the objectives. Sidelaning isn t one of varus strenghts as you have no mobility so no way you can escape(other than ghost summoner spell). But since you have hullbreaker you can melt down enemy towers quite easily.