Hecarim is a nice jungler because :
he have got a lot of speed without boots and can fast arrive in all the part of the map, but the boots help you don't forget to pick it .
he have a lot of AOE skill like Q and E for farm jungle monster.
In the he have got 2 nice skill for gank E and R it can push bask the enemy for do more damage.
The start
You need the blue, if you don't take this kill you can't farm in jungle well, when you reach lvl 3 start to gank for take money, and return to the base when you have enough money for take a part
for equip.
This is all.

Spirit of the elder lizard: for a good farm in a jungle
Boots of swiftness : a good hecarim need a good speed and mobility if you have your speed decrease your damage decrease this is the answer
Youmuu's ghost blade : he give attack penetration, attack , and the active effect is the best for hecarim speed, attack speed
Spirit visage: hp, magic resistance and the passive effect because is a nice combo with w

Don't forget to use Youmuu the movement speed is your attack

The ghost have double effect because he can increase your damage or help you in the escape
The second skill you can chose if you haven't got a nice team take a smite if you are more safe with flash is it or if you wanna be aggressive take a ignite .