Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Just farm minions from your lane. Once you get Tear max out the mana for it before going back, or get close to +1000. Once you get boots of swiftness you can start ganking, it's more annoying earlier because of the slow movement speed but if you feel like you can get around quick enough then go for it, mostly just farm gold from minions. Ask allies to call targets below 350 HP for you to snipe, you've got clairvoyance so once you have them in your camera shoot them. Just take into account a little range because they might either push forward a little or back out behind the tower, tell your allies to try to keep them from pushing.
Keep ganking and try not to die. Be there for team fights and use essence flux to lower the DPS of enemy melee/ranged. Depending on how much you've farmed you should have up to sheen/lichbane.
Participate in team fights and drop towers. After the Bloodthirster the last item is pretty much situational, if you need a blood razor to take out tanks or more attack speed then get it.