What you need to do.
Get a friend that will listen to you. This friend should be comfortable with supporting you. Good supports for this build would be: Lina, Lion, Witch Doctor. Any support that has a high, instant damage output. I wouldn't generally recommend having a Shadow Shaman, just because his ult usually doesn't output enough damage to kill the enemy.
Most builds will tell you to get Moment of Courage first, but you generally want Overwhelming Odds. The reason for this, is that you can do much more damage with Odds pre 6, also, in your first Duels, your high damage support will kill the enemy near instantly.
The Skill Sequence can be modified. I generally have Claritys delivered to me for the way I play. If you or your support are taking a lot of damage, upgrade Press the Attack a few times.
Blink Dagger is a necessity. You should not be farming for any other items, including boots, until you get it. Although, if you choose to spam Odds, a Soul Ring may be effective. If you are terrible at last hitting (like I am) you can generally get it just before, or just after level 6, when you will need it.
If you have blink, this is simple; blink on top of the target, duel, your support hits their ult, and you win the duel.
Without blink, it is slightly harder. If the high damage support you have has a stun, get them to land that so you can reach them for a duel, and the support will ult for the kill.
It is not important that you get the kill, all you want early game is the victories.
Delay getting the tower for awhile, try to get a few duels before taking it. If you see a window where you could gank the mid lane, do so. Your lane is not the only important one. If you see that any other lane is getting attacked, under, near, or around tower, use a TP scroll. Don't be that *******.
Mid late game
So you are here now, let's hope that you have a few victories under your belt. You can be the initiator, or you can do the damage, but the latter would be better for you. If you choose to initiate a team fight, blink on top of where you know, or think an enemy is, and duel. This is incredibly risky, and I don't even recommend doing it. This will only work if your team is well aware of what's going on, when you're going in, and can effectively follow up to the duel. Odds are, you will die doing this. If it is possible, save duel for the end of the teamfight, or grab someone who is about to die. Don't forget that Press the Attack increases your attack speed, so use this on the highest damage attacker, if not yourself, when pushing and attacking.
You should know what to do now
You should be winning, so just keep teamfighting, dueling, and getting rax.
If your team isn't doing well, a force staff can help. If the support has one, place a ward where the enemy team is sitting waiting for your move, have the support stand infront of the team, and force staff one of them into you, where you will then catch them with a duel. Depending on your teams health, and how confident your team is, you can either continue with a team fight, or gtfo.