So, my summoner name is SP3NC3R1000, and I'm only in Silver III. I know that's not good compared to other people, but I figured I may as well post a guide so others can see what you can build for hecarim. I loved hecarim ever since I hit around level 20, and have been playing him ever since (To be honest, I only started playing him because I thought he looked cool :P). My build starts off with his first 3 items giving him damage, and the rest making him very tanky. Overall, hecarim is a really tanky champion, who also has a decent damage output.

These runes mostly focus on health, armour, and magic resist. I also grabbed AD runes to make early game clearing easier, health and mana regen for better sustain, CDR to stack with his q, and movement speed because, well.......he's hecarim.

For summoner spells, I grabbed smite and ghost. I used smite because without it, you can't really jungle, and it stacks well with his w. Now, I will explain why I grabbed ghost instead of flash. Quite a few people usually grab flash because they figure that hecarim's e gives him enough speed to escape. But, it's a lot more effective to grab ghost because you could just use hecarim's ult to jump over walls, and if you pop both his e and ghost at the same time, no one will ever catch you.

Passive - Warpath:

Hecarim's passive is one of the most unique in the game. It gives him the passive of phantom dancer, and it gives him more damage the faster he is. Now, I'll explain to you how you can use both of these passives to your advantage. When being chased down a lane, pop your e, and run through a creep wave. This will make it harder for that champion to catch you because of your speed, and the fact that they need to travel through all those minions. You can use your second passive when someone is trying to take out a tower, and you are at base. Simply pop your e, and with your homegaurds on, when you hit them, they will explode. If they're still alive, turn on your w and spam q.

Q - Rampage:

Hecarim's Q is his bread and butter spell. You grab this first, and max it to maximize your clear speed, and damage potential. Also, the stacks that hecarim gets that give him CDR combined with both the insane amount of CDR already in this build, and all of the passive make him a beast wave clearer, and chaser.

W - Spirit of Dread:

This ability is amazing for his sustain, and if you smite a minion or jungle creep while its on, it heals him. When in a team fight, this ability is amazing, and it can keep him alive through the whole thing, without suffering too much damage. Another helpful tip is to smite a minion or jungle creep when it's up. This returns to you some health, and can save your life during teamfights.

E - Rampage:

This ability is mainly a gapcloser for ganks, or to escape from someone while being chased. When ganking, you sneak up behind the enemy champion, and knock him back into your ally. When escaping, you can use a ward to jump over a wall. Here's an instructional video: https://www.youtube.com/watch?v=80p7LnI1Kz8 Also, when someone is in your base and you already have homeguards, you can pop your e, and run right into them, and they will explode since Devastating Charge deals extra physical damage the farther he has travelled. The most satisfying feeling ever is when their fed Teemo is backing just as you respawn, and you ram right into him. Trust me, they won't last.

Ult - Onslaught of Shadows:

As far as ultimates go, Hecarim's doesn't really do much damage. It's mostly for chasing and the fear for team fights. Position yourself carefully with your fear, and it can be the deciding factor of whether or not you win the teamfight. Another useful thing that you can do is use it for escapes.

Ok, so I explained why you buy those specific items at each back in the item notes. Once you hit level 18, you should have around 3000 health, 200 AD, and 50 armour. Your attack speed should be decently high considering your AD, and if you mix in your q, you NEVER stop dealing damage. Also, you'll be super tanky, so you can just pop e and w, than ult through their team, and take virtually no damage.

Pros:
Great CC and sustain in teamfights
Great initiate with ulti
Super mobile, and almost impossible to chase down
If you snowball, the game is pretty much won
Pretty nice clear time post level 6
Really fun to play, and if used properly, will wreck

Cons:
Not very strong at duelling
Ult is only good because of CC, and barely does damage
Super weak early game, and if invaded, will lose
If low on mana, has to back
Bad ult can get you and your team killed
To be honest, is relatively weak right now, and needs a buff
If he is exhausted, he does a lot less damage for the time being

So, you should start off blue buff and use smite. Then, move on to wolves, and finish them off. By then, you should be level 3 with your smite back up. Finish wraiths using smite, and gank mid lane. Help get first blood, and let your mid laner take it. However, if the mid laner is too far away or has died, take it on your own. From there, take out wight, and gank bot lane. From there, you should back, and take out golems next. Then, gank top lane. Once you've done this, your blue should be back up, so take it. Repeat this cycle or something similar, and gank whatever lanes need your help.

To be honest, I would not recommend you to play hecarim in ranked. Currently, he is relatively underpowered, and most strong jungler (Lee sin, Xin zhao, rengar, etc...) can easily 1v1 him at most levels. He is great for carrying solo que, but playing him in ranked is risky. But if you are confident, then sure go ahead why not?

The ideal team comp with hecarim would have some cc and lots of aoe damage. My favourite team comp with hecarim is with a Sona support, Miss Fortune adc, Katarina mid, and a Pantheon top lane. Together, this can wreck in those teamfights. As long as hecarim has someone else with decent cc on his team, the game will go well.

So, this is my hecarim guide. This build is mostly meant for normal 5v5 summoner's rift, but you could also use it in other game modes too. Hopefully you guys liked it, and if you did thumbs up please. This is my first guide, and I hope that it goes well. I'll try to update this guide whenever there is a change made to hecarim, and I'll read your comments to see what I could improve. So...go play!!!