While some might have played manaless champions before, Renekton's Reign of Anger Fury resource (shared with Tryndamere and Shyvana) can catch many players who are unfamiliar with Renekton off-guard. While he needs Fury to enhance his abilities, he does not need it to cast them. Try to use this to your advantage.
Cull the Meek heals more when an enemy champion is hit; try to use this to your advantage.
Empowered Cull the Meek grants excellent lane sustain thanks to its increased damage and healing cap. Take advantage of this by building Fury, then hitting as many enemy minions as you can in a single swing to greatly increase your health gain.
Keep in mind that the normal version of Cull the Meek grants Fury while the empowered version does not.
Ruthless Predator resets Renekton's autoattack timer, resulting in a possible fourth attack.
When you need to make a quick escape, use Slice into a minion wave or champion. This will trigger Dice, allowing you to use it again and clear distance very quickly.
When moving through the jungle, you can use Slice and Dice to go through some walls. Ideally, try to Slice through walls where you will hit a monster camp on the other side, allowing you to cast Dice for increased chasing or escaping effectiveness.
Slice and Dice can be used to harass enemies who have their abilities on cooldown. Slice in, land a few hits, and Dice back out of range in time before the enemy champion has time to react properly.
Remember that Dice with loaded Fury will activate the bonus, not Slice.
Slice and Dice provides excellent mobility for dodging skill shots in lane. When you see an enemy lining one up Slice through nearby minions out of the way, and then activate Dice to further re-position yourself.
Although they aren't on-next-attack abilities, Cull the Meek and Slice and Dice also reset Renekton's autoattack timer. Try to weave all his abilities in between autoattacks to increase your DPS substantially. These autoattacks also generate Fury, so do not neglect them!
By activating Ruthless Predator during a dash from Slice and Dice's and selecting a champion as your next basic attack, you can dash into an enemy and stun them immediately.
It is recommended to try to reach 100 Fury so you can use two empowered skills. You may activate empowered version of Ruthless Predator and Cull the Meek to maximize your damage and healing, or activate Dice (after Slice) to shred enemy armor, then following with other skill or autoattack.
Elixir of Wrath grants additional damage for your skills and auto attacks, giving additional sustain, turning your already strong early/mid game in a bigger threat, as it can hardly snowball your enemies.
Elixir of Iron gives extra Tenacity to protect or attack the enemies in team fights, bonus movement speed for allied champions, and increased size granting additional range for auto attacks and Cull the Meek. Combined with Dominus, this will make your attacks reach further as well giving Cull the Meek enough range to hit every enemy during teamfights.
Sunfire Cape is a very useful item on Renekton as it synergizes well with his ultimate, adding even more AoEmagic damage. It is also easier for Renekton to get into the middle of the enemy champions due to his Slice and Dice.
Phage gives Renekton some much needed health, and is an excellent choice, as he is pretty squishy without items early and mid-game.
Keep in mind that Renekton does not use mana as a resource, has a built in heal with empowered Cull the Meek, and can build common lifesteal items such as Ravenous Hydra to stay in lane longer. Build accordingly to counter him.
Usually Slice and Dice can be used once, but if it hits an enemy, he gains the ability to use it twice. This will allow Renekton to cover over 800 units of distance. If the situation allows it, don't let him hit an enemy with Slice and Dice, which can be difficult as he can use the ability on minions.
At level 6, Renekton gains the access to use Dominus. It can make turret diving him a very difficult task because he will quickly be able to receive a large bonus of health, which is also essentially a heal that cannot be reduced by Ignite. It will also grant him access to a lot of bonus Fury which can net him a powerful heal from Cull the Meek or an extra-long stun from Ruthless Predator.
Dominus is an extremely powerful ability, especially in the early to mid-stages of the game. The extra health makes a Renekton in this form more durable than most champions. The additional fury and AoE damage can enable Renekton to dish out deceptive and overwhelming amounts of damage, essentially being able to kill two champions by himself easily. Approach a level 6 Renekton with care.
Renekton might choose to build more towards damage or tanking. Pay attention to this: If you force him to build tanky he will greatly fall off late game because of the nature of his kit. If he builds towards damage, prioritize him accordingly in teamfights and be sure to lock him down with crowd control. He has extremely high ability ratios but low survivability outside of health, sustain, and Dominus.
While tanky DPS Renekton greatly loses power late game, he's very difficult to deal with early to mid-game. You should try to isolate him out of teamfights and always know his location.