As a Talon main, here's the basics of playing him. I could give tips on Zed or Kha'Zix, but I'll let others do that.
Talon is a champion that takes little time to learn, but a lot of time to master. Practice him in custom games, starting at Beginning level bots but then go to Intermediate. Work on the combos. Early game for him is essential. If he gets bullied out of lane, he can't snowball, and he'll kinda useless. But if he can, then you'll be an unstoppable monster.
Upgrade his W first. It is an amazing waveclear, it is nice to poke, and you can use it as an escape/chasing tool due to its slowing effect. Later on, when you have Ravenous Hydra, the W coupled with this will destroy so many minions.
Then go for his E. You probably won't need it yet, but always have it ready.
The W and Q are first priority, then the E.
Now for the diving.
Don't just rush in when they're at full health. Early game, you have to farm minions using your W while also hitting the enemy at the same time. Once you've poked them down a bit, make sure both your Summoner Spells are at the ready just in case. Don't make it obvious, and also be sure that you are about in the middle of the lane to avoid turret fire. Make it look like you're about to farm, but then use your E on them. Your damage against them will be increased for a bit, so immediately use your Q. This will deal enough damage to scare the shit out of them. As they're starting to run back to their turret, aa them, use your W, and keep aaing until they reach the turret. If they come back, attack them. If they recall, don't tower dive. Let them recall so you can farm. That way, you'll be able to snowball.
Using your Ultimate:
Your ult is mainly used in three different ways.
-An escape tool. [Invisibility and increased movement speed, very helpful]
-Going in. [Ult beforehand, and then use your E. They won't see you, and that will help a lot.]
-Damage. [This is my main usage of it. Poke them down, then ult in their face. If the blades shooting out don't kill them, then when they converge, that will. If not, it will still do a lot of damage. While you're invisible, keep on hitting them.]
Itemization:
In Order:
Starting:

Full Build By The End (In Order):

Note
If the game gets dragged out, replace Doran's Blade with Black Cleaver, Bloodthirster, or Maw of Malmortius.
Honestly though, it just takes practice not to freak out.
In case it wasn't a given, the Summoner Spells recommended for Talon would be
and 
Hope that helped! If you have any questions, feel free to ask. :)