sigh Riven is a touchy subject. But let's straighten this out first:
- Never, EVER build a SINGLE shred of AP on Riven. Pointless, useless and absolutely disgustingly troll.
- Full lethality also doesn't work well on Riven because of the amount of damage in this game
- Unfortunately.... there IS no "best" keystone for Riven. So it's all play style
Lets get into this now. The most important thing to learn is autoing after every Q (when applicable). Don't just spam your abilities. Your cool downs are longer than people give them credit for. In ranged matchups or matchups where you barely trade, at all, you can take electrocute or aftershock. I prefer aftershock vs the likes of Teemo/Quinn etc.
Since you're just starting Riven, I suggest running full tank set ups so you get a better feel for the champ. Practice with Grasp and aftershock. Once you've got those down, then I suggest using comet and arey to practice your trades. She has a simple trade pattern. If it's someone who has better sustain than you, then it's all about short trades. You want to use QW auto e away for most trades. If you're not in range to Q, then you're out of an optimal trade path. If you have to waste your E to go in to trade on a GP/Gnar etc then that's not worth the trade.
Basically, you only ever E in to people you bully (which is a very few amount of champs this patch in all honesty). Riven loses a lot of match ups early these days unless people really miss step. So you basically want to take every optimal trade you can and then look to hard shove waves and roam. This is really what sets Riven apart from other top laners. The ability to hard shove, roam and pressure the map.
Also, I suggest visiting /rivenmains subreddit as well for more gameplay tips. Watch more videos and practice. Use the practice tool to practice wall jumps and videos so you know where you can wall jump. This is just some friendly advice so I won't get into depth with all of it.
But, for finishing touches we'll go into builds:
You can grab youmuus first for a more roamy play style. If you don't like roaming, get DD for sustain. The normal build path is warhammer into black cleaver. Some people go straight for black cleaver, but it leaves your trade potential and all in... lacking. So a normal build for Riven would be:
Death's Dance > Black Cleaver > GA/Yomuus > Tiamat and wing it from there based on situation.