Having trouble with Hecarim? Here's a guide that should help you understand him. this guide designs a AD Hecarim with a considerable amount of armour to tank turrets or stay in team fights longer. This is also mind you a laning guide. When I jungled with Hecarim it was a full on no for me. (Yes i know Hecarim is a jungle char) This is my first guide so don't be harsh

The runes are pretty loose, it depends on how you want your Hecarim. Hecarim isn't the newest Yi or Olaf. To last long in lanes he needs a considerable amount of HP. I would suggest AD, movement speed, or magic resist runes of the 3rd tier.

For masteries I would definitely suggest 21-9-0. Hecarim does need help with masteries to get effective kills, as I stated before, he doesn't have the best attack damage. You could have some on utility but I wouldn't suggest it. Hecarim doesn't need Vampirism as he has the 'Spirit of Dread' ability, enabling him to farm and also restore health. Executioners calling is definitely needed as it helps get the extra damage you need to kill an enemy before a never-ending chase starts.

Items are very interchangeable. If you're the kind of person who likes to crash tackle someone and kill them in the bush then you might want to get an extra pair of boots to get more damage with Devastating Charge. The Hexdrinker or Phantom Dancer can be swapped for another pair of boots. I would suggest boots of swiftness or ninja tabi.
Additionally an Infinity Edge is a viable option if you're still having trouble with damage.

As the champion spotlight for Hecarim explained, Rampage should be maxed my level 9 as it is your main source of damage. Aura of Dread should be used as when maxed at level 13 it can be as useful as fiddlestick's ult or Karthus's Defile. Devastating charge is powerful at level 3 if a long enough distance is travelled before contact.

Devastating charge is a good initiating skill, after pushed into a lane or something of that kind onslaught of shadows can be used to send them in the wrong way. Then start the chase by using aura of dread and rampage. An effective way of chase killing is to always stay beside them and not behind them, click next to your enemy after every basic attack or rampage.

For high damage I would choose ghost and ignite as summoner spells.
Ignite helps with the reduced health regen and a faster kill, ghost maxes devastating charge's damage which can be effective for early game ganks.

Flash is also a great to use summoner spell. Combined with onslaught of shadows flash can get you through 2 walls, in most cases making it a definite escape.
When using this combo flash should always be used first. If an enemy flashed through the wall and is still behind you use onslaught of shadows on an incoming wall and then you will have a massive lead, enabling you to use devastating charge to gallop away.
However using this combo will leave you with a large number of cooldowns disabling later on opportunities.

Pros
-Great for ganking with a high damaged ally such as Yi or Olaf
-Escape Master ;)
-Onslaught of Shadows can be used to direct an enemy into the team.
-Devastating charge and ghost can be used to surprise tackle an enemy, doing high damage and reaching a max of 701 speed.
-Rampage reaches a cooldown of 2 secs when double stacked.
Cons
-Squishy early game
-Mana hungry early game
-Not strong when performing a solo gank
-Out-jungled by most other junglers
-Devastating charge can easily be countered by CC

I don't like to jungle with Hecarim due to his inability to jungle as good of Warwick or Shyvana. He does less damage and that ability to defend a blue or red buff from being stolen.
Kill the last member of a camp to keep the rampage buff going while gassing it to the next camp.