I'd go in this order then when u buy the Vampiric Sceptor i sell the Doran's Blade i prefer buying a hp potion in the beginning but with the upcoming patch u wont be able to afford it The reason of Frozen Mallet is to be able to lane for longer periods of time and to slow people (obviously)

I prefer using Exhaust and Teleport as he all ready has an ability that is like flash (which sometimes can double). i chose Exhaust for the slowing of characters such as yi or ken for quicker escapes or catching up to them for a kill. Teleport was chosen mainly for begin to mid game because of quick movement to turrets and say u have a teemo or shaco great for ganking.

I'm not an expert at using runes but anything with hp, attack speed, or armor penetration is great for renekton

When having a 1 vs 1 with another champ use cull of the meek frequently and when your fury is available it is great to use Ruthless Predator because of the 3 time hit and stun. If they try to run use Slice and Dice then Ruthless Predator. In a team fight focus squishys (as u can kill them quickly after most of build is done) and take them out. If they are near a turret just Dominus (if available) Slice and Dice, Ruthless Predator then Cull the Meek to kill and dice out. (this champ is great at singling out champs from the other team and killing them)

Renekton is a great tank/ ad champ as i went 23/8/14 with him and sorry if this guide isnt useful for you at all i tried to keep basic since this is my first guide and not sure how to explain completely