Hello everyone! My name is Le monpudding52, and Riven is one of my favorite champions. I've been playing her a lot recently, and I figured I would share my thoughts and ideas with her.
This will be a little bit in depth, so just take it a step at a time. It will highlight laning phase, mid-game roaming, teamfighting, and late game.

[*]High mobility and damage [*]Can get blown up in fights
[*]Has a shield and 2 hard CCs [*]Is vulnerable to targeted poke
[*]Has a strong lane phase [*]Is sometimes hard to use in teamights
[*]Can save teammates [*]Loses duels vs autoattackers like Udyr

This is a beautiful riven guide I found from HD Commentary, go check him out!
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This is the list of basic animation cancels for Riven:
E - any Q
E - W
E - R (activate)
E - R - any Q (activate)
E - R (wind slash)
3rd Q - W
R (wind slash) - 3rd Q
In any of those combos, the abilities will happen at the same time, cancelling the movement of your champion for one of them, but still doing the damage and CC. Play Video Props to FragonHD for this video.

You will have Broken Wings at level 1. When you get into lane and the minions walk down, start going aggressive with Q. Q into them, autoattack. Again. If you don't get the autoattack off, it's ok. Do that for the first two Qs. On the third one, try and hit them and then get about 2-3 autoattacks off, the knockup gives you time. Get Valor second unless you are against a ranged champion. Ki Burst against ranged champions. You have more mobility with E now, so it is easier to close the gap. I often find myself pushed all the way to their tower within the first couple minutes. If that happens, ward the river with trinket, and IF you have teleport, look for opportunities to gank bot lane. Try to bully them as much as you can. If their jungle ganks you, use all your Q charges and E to get out. If you get a chance, try and stun them for extra distance. When stunning them, cancel the animation for it by dashing away at the same time. When you take down their tower or at about 20 minutes, group with your team.

During mid-game, Riven is VERY effective at picking off high priority targets. She has a lot of CC to help her lock down carries. If you find someone out of position, pick a fight with them. Remember not to burn your ult on just one person. If the rest of the enemy team fights your team, activate Blade of the Exile. Get in position to stun more than 2 people or knockup more than 2. If you get a successful stun off, activate hydra and your 3 charges of Broken Wings. As their health gets lower, Wind Slash to finish them off or to get them low enough for your ADC to get them all. Besides fights, group with your team and push towers. You have a lot of waveclear so it is easy enough to push up to towers. You also have a lot of AD to take down the towers.

Like I said before, teamfighting can either be really simple or really hard depending on their team. I already highlighted the individual parts, but this will be more in-depth. When starting fights, YOU are the instigator. Pick fights when you want to, just make sure your team can follow up. Stun them or knock them all up. After you go in, your team can use their CC and AOE to help out. Use all your AOE sources of damage, while trying to weave autoattacks onto their AD carry or mid laner. If you start to get low, try and Q or E out. If you do manage to escape the fight, you can re-engage when your abilities come back up, just make sure you hit your CC so they can't just blow you up. Note you should have Blade of the Exile on during the whole fight. When they get low enough, use Wind Slash to finish them off. Play Video Credits to Best Plays on youtube, go check him out.

If you play the early and mid game well, you should be kind of fed in the late game. Try and pick teamfights if you can. If you have Youmuu's or Zephyr, splitpushing can be a good idea.
If you are splitpushing, use your AOE to clear the waves to push down towers faster. When grouping with your team, it is often easy to get the other team to fight you. It isn't very nice, but you can sometimes bait out angry enemies by spamming an emote like laugh or taunt. If they go for you, just engage onto them. Farm whatever you can, upgrade trinket, get wards down and try and get as big a lead as you can for your team.

That's all I can think of for now, guys. I will probably be adding more chapters in the future or editing the current ones. Just remember, you can use your own ideas too.If you want to take teleport, go ahead. If you want to build Sorcerer's Shoes, go ahead. This is just what I find works the best and is most reliable/consistent. If you have any suggestions or feedback, go ahead and tell me. Thanks for reading!