Long Sword and 1hp Pot
Blood Thirster x3
I grab a long sword and a hp pot in the beginning, this will give you some decent damage on you spear for early game harassing.
Berserker Greaves: this will give you some much needed early attack speed at a low price
Last whisper: attack speed + armor pen, since i go attack dmg rune build the armor pen helps alot
Bloodthirster: 60 dmg + life steal and all that bonus dmg.
Black Cleaver: If the game lasts this long you aren't killing people quick enough. this will help shred tanks with ease, the extra armor pen will also help you teammates do some ridiculous damage late game when you have it stacked to 5.
Early game: grab spear as you first move and get in a side lane. since it only costs 30 mana @ lvl 1 spam that **** to keep your enemies away from their creeps. lvl 2 its you choice whether or not u want heartseeker or stun, i usually go with the stun. reasoning behind this is because its always nice to have a stun to get those extra hits in. once you hit lvl 3 you will have your full combo of moves. Stun + Heartseeker + Spear. this should get people to at least half health early game if not more. Keep harassing with you spear and if the manage to get away from their tower smack them with your combo. Just make sure you are last hitting minions because this build is quite expensive.
Long Sword + Hp pot
Last Whisper or at least the recurve bow and be 500 gold from finishing it
Mid game: By now you should have all you moves and your stun with a few points in it. I usually stay focused in my lane until I have killed a tower if you havent already then you weren't harassing enough. go ahead and kill it quickly. At this point so you can start killing some people. Once i have at least the first tower down in my lane i go to the opposite lane and help them grab a tower, this will be a great time to use you ultimate, wait til you teammates have pushed close to the tower, Leap in there scaring you opponents away from their tower and smack that thing like there was no tomorrow. Once you have a decent amount of towers down and some points into your skills, you will be able to do some crazy damage to people.
Last whisper is you haven't already finished it
Late Game: By now team fights should be the only thing happening while you push the last of their towers. Now is when you need to decide whether or not u need to build some other things besides bloodthirsters. Most games you can build 4 of them and be fine. If their tanks are giving you a problem then you can buy a bloodrazor instead of one of those bloodthirsters. If it seems that you just aren't killing things fast enough you can switch out a bloodthirster for Black cleaver. this makes it so anyone in your way usually dies, and regrets trying to stop you.
Some Tips For Team Fights:
1.You defiantly don't want to be the first one in there. you are going to be pretty squishy all tho you lifesteal most of the time thats not enough.
2. Make sure you are using you 3-peice combo: Stun > Heartseeker > Spear with your attack speed you will do some ridiculous auto attack shots within your combo.
3. If you get a chance to use your ult once everyone has engaged, make sure you are in a bush or far away when u begin to cast it so they dont automatically run scared of the insane dmg you are going to be doing if they are in the middle of your circle.
4. U can use exaust after your ult has channeled to keep someone in your dmg radius. also if you switch out flash for ghost you can change where your point of impact is with your ult.