In the early game you need to be farming your Siphoning Strike. Creep kills are important But that means that you will need spirit fire to farm better. If you can get a top solo lane then you should be able to farm till the 7 min or so then you start ganking. Or whenever you have your Wither at lvl 2 . Also its key to get mercury's threads only for the tenacity. it will be key late game for teams with a lot of stuns taunts and slows. You should aim for 80 creep kills by the 10 min. That is average you could do better or worse but aim for this.