In late game, You can sell "Malady" and buy "Lich Bane" and also sell your Phage and buy "Rylai's Crystal Scepter" You can also sell your ring and buy "Nashor's Tooth".

Toxic Shot
You can easily farm with your Toxic Shot and your Attack speed from Malady, Berserker's Greaves.

Noxious Trap
Can be good for big waves, but try to put the Shroom between the "Melee" and "Range" minions, Then it will hit all of them.

Blinding dart
In the start of the game (1:40 - 15:00) you can use it to farm, But its often not necessary.

Move Quick
Meens nothing when farming ;)

Game Style
Is the most important thing. You're going to play as a P*ssy, You're just going to try Haraz your opponent. Try to hit them with your (Q) = Bliding dart just after you've hitted them with your (Basic Attack) + (Toxic Shot).