First and foremost, the main thing you should know about Renekton is that your cooldown and fury management will make or break you in every single encounter. To start off, grab yourself a handy-dandy Doran's Shield, or a Doran's Blade if you're feeling ballsy. Buy a health potion and a warding trinket and make your way to your new home. Before the waves come, you'll want to keep an eye on your blue/red (depending on which team you're on) to help discourage invades. Switch between standing in your river bush and roaming to the first bush close to your buff to ensure no baddies are afoot. Once the waves connect and the invade either never happened or has been repelled, go ahead and put your ward in your river bush (As far as possible away from you, but still in the bush, to give maximum vision range.) Make sure to start with your Q to give you the early game sustain that Renekton so desperately needs, and farm defensively until you reach level 6.

Now that your lane opponent is hopefully being pushed back towards their tower, it's time to put some pressure on them. Return to base at ~1600g to Purchase a Vampiric Scepter, Boots, a few health pots, and 2 Stealth Wards. Place a stealth ward in the round bush near baron, and one in the opposing tri-bush, and keep your trinket ward in your river bush. Once you get back to lane, ask your jungler to come up behind them if possible after they're closer to your tower from your absence, and dive in on them. Start your engagements with your E, then W to stun, E again if they begin to run, and Q as often as possible. If you believe you'll get a kill from your efforts, use your ultimate just before your E to maximize your damage done. With a little luck and some skill, you're earn you or your jungler a nice kill, and you can now start to roll your lane.

Now once you're around level 10, you'll want to finish off your Ravenous Hydra and be starting on your Sunfire Cape for that delicious armor. Obviously upgrade your boots ASAP as well, as there's no reason to be slow in League. (Get Ionian Boots of Lucidity if you're doing well, or Ninja Tabi if you need a little more beef to handle a strong opponent.) Now that you've made your presence known, it's time to roam every once in a while since, in theory, you're pushing your lane fairly well. Ganking mid with a well-timed W stun can give your team a serious advantage, and net everyone some global gold from knocking down the first tower. Just be sure not to leave your lane for too long, as if for example Nasus gets to farm for a while, he's going to become an unstoppable goliath made of armor and your tears late-game. Just keep an eye on things, one of the biggest things in this game is map awareness.

Now that your laning phase is over, you're going to want to patrol mid and the jungle around your lane, ensure that your towers aren't being pushed. If your jungler allows, try to grab red buff as much as possible, or deffer to your ADC. Make sure you have some meat on your bones, because in fights, you're there to absorb damage and push their team like a steamroller. You can't do that if your armor is made of toilet paper. In team fights, unless you have a Xin Zhao or other tanky jungler, it's usually going to be your job to engage team fights for your team. So as you engage, Hit your ult when you feel it's the right time, and E into their team, W'ing and focusing their ADC/APC/Support. Always use your stun on the ADC or APC, as they're the main sources of damage, and as such need to be shut down early. Try and keep their support and tank busy and away from your team, and they can get quite annoying with their CC and whatnot.

It's late game, so in an ideal game, you're already going to be a monstrosity that nobody will want to risk fighting. This is because A: You have plenty of health/armor/magic resist, and 2: You have good management of your cooldowns/fury and know when and when not to harrass/dive/back off. If you've found yourself dying a lot, now might be the time to invest in a Guardian Angel, you'll need to survive to make those final pushes to their Nexus. End game is where throws count the most, so be very cautious, and take as few tower hits as possible, while keeping pressure on their team to keep them from stopping your adc/jungler from melting towers. If everything goes as planned, you should be able to shatter that shiny blue or purple crystal and bring home the W. Congrats, you've successfully done your job as a top laner!