Hey my name is C-Only.
The only reason that im making this is to have my own build when I don't remember what I have to buy.
This isn't a "PRO" guide but It's a build I'm owning with :-) I hope you can use this if you find this build/guide.
Have fun out there.
-Only

Your best chance to get a FB is at lvl 3.
you want a high dmg range or melee+range(like yi, taric, mundo etc.) to lane with.
when you use your slice you want to stun, ignite and then exhaust, and then dice to finish them off or if they actually get away.
if you are playing with one of your friends he might want to have heal.
If he use ignite or exhaust then you can use heal instead of ignite/exhaust.

With this high combo of dmg and slow its pretty easy to get the first blood.

My best FB's with Renekton is so far lvl 1 with Jax(read Renekton's Best Friend!), and a first blood at lvl 2 with mundo and then a double kill at lvl 3 right after.
With a killing spree at lvl 3 you already got alot of gold and more exp. with the potions you dont even have to go back and you can just keep farming which give you a big advantage!

Ignite
Igniet provides great help in the beginning and late in the game to finish off the enemy.

Ghost
I prefer to use ghost as combo for the ultimate to make sure you get close to them and you dont waste your ulti.

You can also use a combo of Ignite and Exhaust to make sure they dont get away and make high damage at the same time.

I prefer full AD and some armor, but use the runes you prefer to use.

But i made some for you guys anyway..

ofcourse strenght runes to make high dmg and then some defensive runes to keep you alive as much as possible.

you might want to ask why i want Seal of strenght instead of Glyph of strenght?
Because Seal give more AD... I dont remember how much it is but its like.. 20 to 40 AD.

You want to start out with stun(predator) to make sure you have enough time to make some dmg and then run away again(at lvl 2 with Slice and dice).
Then you might want Cull the meek to make damage and life steal.
A great idea is to slice in, stun, cull and then dice out.

Ulti and Ulti combo

When you have your ulti you want to use ghost if you want to run after them or use the Exhaust+Ignite combo to slow them down and make high damage.

So far the best champion combo i have tryed is Renekton and Jax! with the 2 stuns and high dmg+you both are able to jump then you are the ultimate 2-man-army!
Easy to get first blood early in the game (lvl 1 or higher)

Early in the game you want to damage all the minions and then finish them all with Cull the meek.
At higher levels you want to slice in, Cull the meek, and then finish them with dice.