In toplane, there are three great bushes for you to hide in. Until around level 3, just cs from the bush and use Q > jump to poke. With your dorans, you'll have lots of sustain and damage to work with, and you'll be ready to properly assassinate someone.

So, to successfully assassinate someone, you have to have the right combo. To assassinate from a bush, activate Q, E them, and jump on them. Use your empowered Q and your W to finish them off. If they aren't dead yet, never fear! Just use your tiamat/hydra's active or a few basic attacks.

Now, you want to assassinate someone using your ult, even in the middle of a teamfight? That's easy as well for Heart Hunter Rengar! Just activate your Q, jump on them, W, then Q again. Your W is great because it gives you bonus armor and magic resist. Now tha tyou're in the middle of their team, what are you going to do? Well, that's easy. Just auto attack a lot and spam your abilities. Your tiamat/hydra will do the rest for you.

So, you're trying to assassinate someone, maybe with your ult, and they're running away? That's why you have youmoo's ghostblade.

Tiamat and Trinity are pretty self explanatory: Tons of damage.

People are probably going to be stacking armor against you, and you need to stop that. That's why you have your last whisper and black cleaver!

And to be honest, Rengar doesn't really need boots. If you want, you could just get a tank item instead, such as Randuin's. I do like to get mobility boots on him, and Merc Treads are great to stop you from getting wrecked by CC when you jump into their team.

I hope you enjoyed this brief Rengar guide, and happy hunting.