This is my first guide and appreciate feedback and comments as well as your votes. Try out the guide before posting please.

This guide is made for the Twisted Treeline map. This is where I feel Hecarim is the strongest (versus Summoner's Rift) due to the movement speed buffs on the map.

Hecarim is a great champion for ranked 3v3 due to his tank y ness and ability to move quickly. To explain a little I take clarity in 3's a lot for sustainability. Remember there is no Blue Buff here folks. Building defensively will allow you to take part in fights by fear ulting your enemy away from his own turret, or by ult splitting an apposing team and taking heavy damage initially. Make sure when you use this as an initiator that you get your Spirit of Dread quickly so that you regain your health back from the initial starting blows. With just a few offensive items a long with your Sun fire Cape passive will give you amazing ability in team fights. With your increased movement speed you should be able to pick off any stragglers that haven't quickly backed to the base. You can play this champion multiple different ways as far as laning and starting positions. The strategies my team runs the most are as follows: Start by going to the bottom bush for a level 1 team fight if your team feels strong enough against the enemy champions. Hecarim should be able to easily get 1 kill in this fight because someone is bound to try and flash run away but with your movement speed quints and your boots to start, well.. they shall quickly meet your scythe in death. You can either start jungling from level 1 (with help of your team of course since you do not have smite) or you can solo top and once your carry on bottom feels up to it he can switch to top while you start focusing on clearing jungle and buffs full time. The most used strategy by me is going to bottom lane while a squishier teammate farms top to level quicker. This strategy requires another bottom laner that is tanky and can handle solo laning after you have gotten your wriggles or at the very least razors to start full time jungle. Remember that your Onslaught of Shadows WILL allow you to go through walls, for example from dragon to top lane gank - Red to top or bottom gank - or any wall that allows you to massacre the enemy. Keep your eyes aware of the map to find enemies out of position and make sure you always get your speed buffs that are up. As Hecarim can quickly move around Twisted Treeline to exploit the weakness of the other team.

The heavily defensive hybrid mastery will allow you to stay alive and initiate team fights. Noteworthy mastery points are:
Runic Affinity - Utility (keeps you strong with buffs)
Swiftness - Utility (moves speed = attack damage)
Summoners Insight - Utility (clarity)
Tough Skin + Bladed Armor - Defensive (jungle sustain ability)
Summoner's Wrath - Offense (ghost)
Weapon Expertise - Offense (damage sustain ability without relying on offensive items)

Armor Penetration Marks will allow you to hit hard with little offensive item focus, meanwhile your armor will keep you alive long enough to kill them with Rampage + Spirit of Dread. Don't forget Hecarim's passive Swiftness Quints are just as important as the Armor Penetration Marks.

Controversial substitues
Sunfire Cape - Aegis of the Legion - Warmogs Armor
Wriggles Lantern - Bloodthirster
Maw of Malmortius - Atma's Impaler - Force of Nature
Frozen Heart - Shurelya's Reverie
Boots of Swiftness - Ninja Tabi - Ionian Boots of Lucidity - Mercury Treads

Use your clarity when it's up and spam your abilities to quickly run across the map and quickly get a lead in cs. While laning do not use your Spirit of Dread to push the lane quickly if you do not need to, Spirit of Dread combined with Rampage will quickly make work of minions and you will be pushed to the tower in no time with the whole enemy team pushing hard aggro onto you at this point... luckily Hecarim is very good at eluding.

Remember that fearing will make your enemy run away from you. Once you have initiated and have one split make sure to get behind that enemy and use Devastating Charge to further push the victim into your own teammates (try chaining a stun with this if he's not dead yet)

Warpath (Passive) – Hecarim ignores unit collision and gains attack damage equal to a percentage of his bonus movement speed.
Rampage – Hecarim cleaves nearby enemies dealing physical damage.
Spirit of Dread - Hecarim deals magic damage to nearby enemies for a short duration. Hecarim gains health equal to a percentage of any damage those enemies suffer.
Devastating Charge - Hecarim gains increasing movement speed for a short duration. His next attack knocks the target back and deals additional physical damage based on the distance he has traveled since activating the ability.
Onslaught of Shadows (Ultimate) - Hecarim summons spectral riders and charges forward, dealing magic damage in a line. Hecarim creates a shockwave when he finishes his charge, dealing additional magic damage to nearby enemies causing them to flee in terror.
Devastating Charge will damage turrets.
Onslaught of Shadows will go through walls.

Since his first sighting on the northwestern shores of Valoran, the towering, armored specter known as Hecarim struck a chilling fear into the hearts of all who laid eyes upon him. No one had ever seen anything like his titanic, ethereal form before, and the mystery of his sudden arrival was deeply unnerving. When Hecarim began to march eastwards, leaving a trail of desolate, lifeless ground behind him, the villagers of the plains fled their homes for the safety of nearby Demacia. In the city's now-overcrowded taverns, rumors about this inhuman phantom spread in hushed whispers. Some claimed that he was the vengeful shade of an ancient warrior, intent on destroying all living beings; one man insisted that they had seen him leading an entire legion of spectral cavalrymen; others still believed him to be the creation of some hateful necromancer. One Demacian commander, seeking to dispel the terror that had gripped the city, assembled a few of his finest soldiers and rode out to turn back or destroy Hecarim.

The commander led his soldiers to stand in Hecarim's path and braced for his assault. As the apparition bore down on them, an overwhelming sensation of dread gripped the warriors. The men, frozen in fear, could only scream as the ghostly titan ran them down, tearing them apart and trampling them beneath his iron hooves. Hecarim turned to the crippled, cowering commander and uttered a chilling statement: ''This is merely the beginning. No mortal army can withstand the might of the Shadow Isles.'' With that, Hecarim departed, resuming his grim march. Driven to insanity by his nightmarish experience, the commander stumbled back to Demacia, where his dire warnings were dismissed as the ravings of a madman. While Hecarim's origin and intent were still a mystery, his destination became clear when he reached the Institute of War and, in a voice both ominous and commanding, demanded entry into the League of Legends.

''You don't understand...the shadows will consume us all...'' - Former Demacian Commander