Marks
Attack Damage marks boost Renekton's already strong early game damage. Strongest levels 1-3
Armor Pen marks sacrifice some of Renekton's early game power in exchange for a stronger mid/late game. Strongest levels 4+

Seals
Flat armor is the way to go against AD opponents. If you are playing against AP you can swap these for scaling amour or scaling health.

Glyph
Flat Magic Resist glyphs are 100% needed against an AP or Hybrid damage opponent.
I love going 6 CDR (5%) and 3 Flat MR (4) or 3 Scaling MR (9) against AD opponents or weak AP opponents.

Quintessences
Very much the same as our Marks get AD for early game or Armor Pen for mid/late game.

Because Renekton is an AD caster your trades rely on his abilities and how you use them. The basic trade is Slice and Dice-> Cull the Meek-> Ruthless Predator-> Slice and Dice in this trade you dash in Cull the Meek-> Ruthless Predator and dash out to safety. This trade works well but to use Renekton to his fullest you must weave auto attacks into your trade. A full trade with auto's looks like Slice and Dice->AA-> Cull the Meek-AA than Ruthless Predator right away because it resets your attack then one more AA before you use your second Slice and Dice to leave. This trade takes under 4 seconds and chunks your opponent while not allowing him to trade back any damage.

When going in for a trade the more rage your have the better, always try to have at least 50 rage so that you output more damage. If you are at 100 rage you trades and do almost 50% of most enemies hp before level 6.

Now how do you determine what ability to use that 50 rage on? Well it depends on the situation, almost always you are going to want to use your rage on empowered Cull the Meek's because the heal and AoE damage is so great. Empowered Ruthless Predator are great if you need to lock down someone longer or are trying to burst down a single target. Empowered Slice and Dice is something you don't use often, only use empowered Slice and Dice's when you have a heavy AD team comp and you can land it on at least 3 enemies.

When in lane don't just waste your fury to push the wave, just having a full fury bar will be enough to zone your opponent most of the time. This is your key resource don't throw waste it unless you really need the sustain from Cull the Meek.

I hope this guide helped you become a better Renekton player!