Renekton is a very fun champ to play, but his biggest issue is cooldown, and early game squishiness. To counter this, you go offensive quits and reds, and armor yellows, and mr blues.

Your build will go CD - Health/CD - Damage/CD - Damage/Lifesteal - Defense - Defense

Because of your runes and the brutalizer, you have a great amount of armor pen, which allows you to pick on opposing players early and late game. Stacking a Bloodthirster makes sense, because you wont be able to stack much AD with a defensive build, and the lifesteal pays off.

Q First, W Second, E Last, leveling your R whenever possible.

Youre malee, exhaust and Ghost make sense to use with renekton, hes slow, and getting that early exhaust on someone can make them way more gankable early game.

To initiate a fight, go R-E-W-Q-E