I have hundreds of games on Hecarim, he's one of my favorites. The best thing I can say is that Hec is the true definition of a flanker. The most powerful fights I've had come from a wicked ult from the side or behind. There's a lot of rune setups people run, but the one I've had the most success with is Predator, Sudden Impact, Eyeball Collection and Relentless Hunter. The secondary runes are a toss up between sorcery or resolve. I take sorcery for celerity and and gathering storm, which will help you out at the late game. Hecarim's early game is not good so you'll want to either power farm or go for ganks a lot using predator. As for items, personally I go cinder hulk into a tri force if i'm doing well, or if you're falling behind, itemize against the fed opponent. So usually cinderhulk<triforce<sterak's gage<dead man's plate or spirit visage<spirit visage or dead man's plate<adaptive helm or thornmail.The best tip I can give is to be all over the enemy mid or adc like glue, even if you die if you can take down a big part of the enemies damage, it's worth if it helps your team win the fight. Make them waste the flashes and ults on you so your team can move in for the kill. I also max Q,E,W in that order.