It's pretty straight forward, you run into things and spin, they die, unless it's Darius cause **** Darius.
Just don't play this against a tanky team.

You almost have to start with Gromp -> Blue buff since he demands a lot of mana with his Q.
He has some of the best ganks in the game with his speed after he gets Swiftness Boots and his R is great for chasing under turrents of ganking over walls.

Pros:
-Insane damage.
-Without great escapes it's impossible to run away from him when you're using stalker's blade.
-You get more out of your ult since you can usually kill at least one champ while they're feared.
-Lots of CC with your R and E so it doesn't always matter than you don't have much tank stats.

Cons:
-If you're playing against a tanky team you might not be able to take them down quick enough, so as I said earlier, don't play this against a tanky team, play it if you see that their team is pretty squishy.
-Stuns are very effective on Hecarim, but this can be fixed with scimitar.

Just try to hit as many people as possible with your R, but don't use it to jump from straight forward the enemy team since he's not invulnerable while he uses it and can still be rooted and stunned.
Other than that he's a great team player since he can just R in to start a team fight then ram right into the enemy ADC or assassin to kill them with your burst.