Talon is not a constant combatant. He is an assassin, and this build is to serve that purpose. You will do a lot of damage all at once, and keep your opponents won't have the chance to escape. You will become a killer, but NOT a fighter. Attack DAMAGE, not attack SPEED. Do not play this build as if you are Master Yi. Running headlong into battle will get you killed - fast. You won't need attack speed, because you won't be hitting people over and over. Bide your time, wait for an opening in the enemy's defenses, then jump in and hit them with every move you have, and walk away. If you play as a constant aggressor, you will feed the other team. So be careful out there.

The items listed are in order of purchase. In general, don't bother buying parts of one item and parts of the next. Finish one before moving on to the next.

Regrowth Pendant is a great starting item for Talon, as he is squishy. You should attempt to only enter combat surgically, bide your time and wait to jump in. But the few hits you take will hurt, so regroup at your turret for a moment and your health will come back fast. This will allow you to lane ceaselessly early game and make enough money for the expensive build. You should sell the pendant when you are a high enough level (apx 10) that its effects become unapparent. Try to at least have an Infinity Edge by this point. I often will sell my Regrowth Pendant to pay for the final piece of the Infinity Edge. I do NOT recommend Doran's Blade. It does not have enough lifesteal to keep you in the fight early on, and honestly, you shouldn't be in the fray constantly enough to see any returns on it anyway.

The Mercury's Treads are so that you can get into battle, make your kill, and GET OUT without being trapped.

Take the basic boots and then use your regrowth pendant to lane long enough to buy your BF Sword. Once you have it, you can start killing your foes. At level 7, +45 AD is amazing on Talon because not only will his base attacks improve, but all of his abilities are AD as well.

Then finish Infinity Edge and Your boots. I recommend Infinity Edge if you can afford to, boots if you can't.

Now that you are dealing a mess of damage, grab a Bloodthirster to deal EVEN MORE. Plus you get the benefit of lifesteal, which is important since you no longer have your regrowth pendant.

Once you have that, it's time for the Youmuu's Ghostblade. This will help in pretty much every way for Talon. Especially the cooldown reduction (allowing you to comfortably blow your Ult in EVERY battle) and the move speed bonus, allowing you to take any enemy by surprise or run them down effectively. But remember to USE it, because if you don't then its only about half as useful.

Now, if the enemy is smart they will have taken some armor to counter your AD. If this is the case, or if there are tanks, go buy a Last Whisper, to get around that pesky armor. If they haven't bought armor and you have no tanks to deal with, buy another Bloodthirster! You can't have too many.

The final item is up for grabs. Banshee's veil is good if people are focusing you, which they will, because you're destroying them! If for some reason the other team is not smart enough to focus you at end game, get either another Bloodthirster for damage, or get a Phantom dancer or Frozen Mallet if people are getting away, or Trinity Force if you like sheen's effect. You'll only get a bonus 162 damage from it, so a second bloodthirster is my recommendation, as it doesn't have the 2 sec cooldown. But any of these choices are good ones.

Rake: Take Rake first, and max it first. This ability allows you to harass aggressively early on from a safe distance (as safe a distance as Talon can strike from). It is also useful for farming minions, both as a last hit or if you have phantom dancer, you can use it on fresh minions and then just run in and clean them up by last hitting each one quickly.
During a fight Rake is your go to ability. Since it is ranged you can use it often to harass, and since it causes slow, it makes for a great final attack and if it doesn't kill them, you'll be able to run them down and finish the job.
Early kills with Rake: Because rake does good damage and causes slow, an early kill is easily achieved if you are laning with a champ who has any control ability, or with a champ who can break armor, such as Wukong. So if you wait in the bushes, when the enemy gets close enough, Wukong can jump on them with a Crushing Blow, lowering the target's defense, and you can instantly hit them with rake, slowing them and allowing you both to get enough hits in to get the level 1 kill. Having flash is also useful here as you can make your escape afterwards. Chances are you'll be a little dinged up.
Harassing with Rake: Rake is Talon's ranged attack. It is a skill shot, but because the blades fan out it is very easy to land hits. Also, be aware that its range is slightly further that the in game aim assist would have you believe. So use it often to keep enemies at bay while simultaneously farming minions. Get as many minions with rake as you can, but be sure to target enemy Champs.
Cutthroat: a wonderful move, but for the majority of the fight, you only need 1 rank, since its silence doesn't get better, and it doesn't directly cause damage (though it does make subsequent attacks do more damage). So take it 2nd, but max it last. It is a teleport that places you directly behind an oponent, silencing them and amplifying your damage against them. You'll mostly use this to initiate a surprise attack or end a fight with a fleeing enemy. It's also useful for escape, as you can use it on an enemy minion to get distance from an enemy champ. It also combos well with Flash. If you use Flash and then Cutthroat, you can cover a great distance very quickly. It also combos amazingly with Talon's other abilities, and I will get into that within the other abilities.
Noxian Diplomacy: the reason you don't max Cutthroat earlier. Take it third, max it second. Noxian diplomacy makes your NEXT attack do more initial damage, plus it causes bleed and makes enemies unable to hide. So, you can actually activate Noxian Diplomacy and then use Cutthroat on an enemy, teleporting you to him, buffing your damage, and then inflicting maximum pain, and preventing him from going invisible. So by maximizing Noxian Diplomacy, you are actually making Cutthroat more effective. Plus it can be used very often, and doesn't NEED to be combo'd with anything else, though you should when you can. Be sure to use Noxian Diplomacy on any enemy that can stealth, such as Twitch, Teemo, or even another Talon! Watching another talon use their ult while not actually invisible allows your whole team to dodge the second part of his attack. Which leads us to:
Shadow Assault: This is Talon's ultimate, and it has many uses. It has an initial radial attack as your blades shoot out into a circle. It also causes you to become invisible and gives you a huge increase to movement speed. After a short time, you will reappear and all of your blades will tear through enemies on their way back to you. One important thing to note about Shadow Assault is that the blades will return if you press R again or if you use another ability. This is actually very useful as it allows you to use cutthroat to teleport BEHIND an enemy, and upon appearing behind them, your blades will tear through them to get to you. You can do this same thing by using flash after activating your ult, allowing you to hit any enemy you wish within the vicinity, even fleeing foes. You can use this combo to initiate combat, and since noone will see you coming, you can: Shadow Assault, run in, Cutthroat an enemy, Noxian Diplomacy, then Rake. If they are somehow still alive, they'll be slowed from rake so you can catch them and finish them off.
Also, Shadow Assault is a wonderful quick finisher, since it's radial attack is instant. This is useful if an enemy goes invisible near you to escape death, you can activate Shadow Assault and it will instantly attack in every direction.
Finally, and perhaps most importantly, Shadow Assault makes for a great escape. It makes you invisible and gives you crazy move speed, so you can get away. However, do not just stop in the bushes, as the blades will give away your location.

Always take flash! You can use it to catch prey, escape, or most importantly, you can combo it with your ult to hit anyone in the vicinity, even if they're running!

Your second ability should either be Exhaust (for either offensive OR defensive use), ignite (for obvious reasons), or teleport. I recommend teleport for three reasons:
1. Makes it easier to organize a gank, and you should be focusing on ganking.
2. Allows you to lane more often, helping to pay for the build.
3. The sudden, surprising addition of Talon to any fight is huge.

At level 10, you shouldn't bother laning so much, focus on being a roaming ganker. Move from lane to lane, waiting in the bushes and picking off champs who have no idea you're there. To take your prey off guard, either cutthroat into the battle or even Shadow assault while in the bushes and then cutthroat, to start your attack with massive damage.

Using Noxian Diplomacy and Cutthroat on an enemy who pops in and out of visibility (such as Akali) can be very useful to make them visible to your teammates, thereby removing their advantage.

Talon is a TEAM PLAYER. Since his survivability is extremely low, be sure to have at least one other person around before initiating combat. In fact, try to always let your teammates initiate combat.

As an added bonus, you can use Noxian Diplomacy's initial damage boost against buildings. That, coupled with your high AD and attack speed, you should be able to cut down turrets and barracks quickly.

If you are running from someone, and you think you could kill them, ult->cutthroat->noxian diplomacy. Or any combo of that so long as you can use cutthroat. The silence can give you enough time to either get the kill or run away if they can be otherwise occupied by an ally.