1. Prime one Q out of sight of your enemy, this begins the skills total cooldown. use a second Q as you wait to ambush. Q into the fight - your Q should have almost reset. This can add burst to your combo's and trades as her entire Q sequence will be up soon after your 3rd Q is used to initiate - with more CDR this is more effective.
2. Prime 2 Q's before a fight. Flash into an opponent and cast your Q mid-flash for a CC heavy engage, follow-up with W - this can help engages where you need CC and can't afford to wait for cooldowns. Your Q's total cooldown will also start counting down once you prime your first Q so it will also allow you to CC again with a Q-Q-Q combo during the fight sooner than if you initiate with a non-primed Q.
3. For a faster, shorter Ranged Q, cast your 3rd Q during a Dash and it will be shorter ranged and impact the ground sooner. This can be useful if your W is down and you need CC and fast! Saving your E until your 3rd Q can make this combo worthwhile and it can be a lifesaver for your 3rd Q to hit the ground faster, if you are exceptionally good you can also use it to throw off an enemies timing and perform a spell interrupt faster than they expect, as well as an auto-attack interrupt.
4. When you activate your ultimate, a brief spell animation ensues - casting dash or Q immediately cancels this movement inhibiting spell animation and can get you on your way to gap closing slightly faster!
5. Ravenous Hydra - this item resets your attack animations when used, so if you activate it immediately after Riven executes an attack, Riven will be able to attack sooner! This can be useful in clutch situations and this item has the same interaction for all Champions.
6. Ki Burst can also be used to cancel Riven's Attack animation like the active of Ravenous Hydra - keep this in mind as using Ki Burst immediately after you have landed an auto-attack will allow you to auto-attack much sooner.
7. Implementing attack commands between skill animations rather than allowing the animation to complete can significantly increase Riven's damage output, simply Cast a skill - say, Q - and quickly input an attack on your target, this will allow her to perform an attack before the Q animation has completed and if stringed with her whole Q combo and quickly can cause you to deal much more damage much quicker than if you simply Q, then wait for the animation to complete and then auto attack. With practice this can allow Riven to perform a bursty combo so fast the enemy wont be able to react.
8. Ability cancelling - Understanding that your Dash and Q cancel your Ultimates first cast's animation is useful, it is also useful to know stringing together this along with Hydra's active and her Ki Burst can allow for a significantly faster bursting of Champions because they cancel her animations too; for example - Dashing into a fight and activating R, then triggering Hydra cancels her ultimate's activation, Hitting W cancels Hydra's Animation and hitting Q cancels her W's animation, knowing this can let you burst down enemies in team-fights much quicker than if you let the animations play through and simply right-clicking wont cancel her animations.
9. Valor - Riven's Dash allows her to move through certain terrain such as Jarvan's Cataclysm and Anivia's Crystallize.
10. Riven's Q's 3rd animation allows you to jump certain walls, this can greatly improve her utility and can be great as an escape mechanism or to initiate fights.
11. Riven's Broken Wings 3rd Q can be used to cancel Riven's Wind Slash Active animation, Keep this in mind as it can help in situations where you need to gap close sooner to make sure an enemy is dead.