During the early you are going to want to farm up that Sheen as fast as you can, in my experience it is one of the best items for you because you can proc it every time it is off cooldown, also the extra mana will help you since you are a little scarce on it early game. Speaking of mana, feel free to spam your Q whenever you want but just keep an eye on your mana level and try and keep it above 50%. You can use your Q to harass or to get cs. Keep continuing to farm but if you see a chance to get a kill take it, but the time you are level four, you should have all your abilities. The combo I use is: Activate your charge prematurely so that it charges up and increases the damage output, then use your Q, and then use your W (Note: Remember to use your Q whenever it is off cooldown because the more you use it, the less time it takes to cool down).

By mid game you should probably have your Trinity Force farmed up because in my opinion, it is basically his only core item. The rounded stats along with its passive give you the tank ability and damage you need to survive team fights and land kills. Now that you are past level six and have all your abilities, your combo changes a bit. Usually I use my ult whenever there are more than one person around but if you think you need it then use it. One thing to remember though is that it will only fear the people in the AoE shown, not the entire span of the ult. After you land your ult, use you Q and then W, remembering to use your Q whenever off cooldown. The reason I don't use the E until I have to is because it was used as a gap closer but now that you have your ult you should use it to chance down your enemies is they try to run away.

In the late game, nothing really changes with the combo, it is still the same except for the fact that you should try and fit as many basic attacks as you can into the combo, this allows you to proc your Trinity Force more often.

This item I find is completely optional, I think its cool because it gives you more life steal and spell vamp and makes your w more effective. But that's my opinion, If you think that you need more tank ability or more damage, then you can trade that in for a Warmogs, a Blood Thirster or another Phantom Dancer.

Pros:

Good Damage output all game
Not mana dependent
Amazing passive
Pretty OP
Can jungle
Pretty easy to play

Cons:

Requires good farm to do well

Note: When you are farming, make sure to last hit and not just auto attack. If it is hard to get last hits, make sure to pick up a sheen and use your Q, the bonus damage from it will help you get better last hits.