The best way to learn Riven is to face a Riven. It's then you see her strengths and weaknesses. I've played against a lot of them and I've picked up a lot about her, but I still refuse to play her.
Typical combo goes Q AA Q AA E Q AA W AA R and if you aren't dead by that time, you saw it coming and have high mobility or tankiness (Which is what you should have if you are top anyways, says Gnar player).
I've seen most of them disregard health items but the most Annoying Riven players were the ones who build AD tank items like Steraks, Black Cleaver, and Maw of Malmordeous. They weren't squishy enough for me to burst down normally and they usually played decently compared to the tryhards I usually faced.
Another tip I gave to someone else: Play support for a while. Just like, 2 weeks. Try to teach yourself map awareness and the best warding spots. There's a quote "Top lane is an Island." You will probably be alone up there. Expecting a gank from the enemy jungler is terrifying, but having the awareness and vision (Which by the way, Top is just a reflected bottom, which everyone should know by now) of a support, you should know where to best ward and keep yourself safe when your jungler is out of reach (Or in your division, has everyone muted).