How to lane against Riven

Riven's damage depends on her hitting you with her q and her auto attacks in quick succession, so don't let her do it. Ranged champions can do this easily since they can poke from a safe range, but any melee champion with an escape or stun can break up her combo by staying out of range after she's used abilities and before she can auto attack. Keep track of your positioning, she's going to want to get close to you so she can hit with her first and second q and still use her e to escape or continue the engage, but if you force her to use them purely to close the gap she will lose damage, so with all that in mind stay far enough away that she has to use abilities to get at you. In addition to all of this, she'll probably want to use her abilities to push the wave or get easier last hits, so wait a few seconds after she uses her last q hit to let the buff fall off and use that time to punish, since she'll have little damage to throw back at you (you should get used to waiting for your opponent to use their key moves this way before engaging against any champion).

I main Riven. Most of her power is in the utility, CC, and mobility of her kit. Like most AD casters, she builds AD/Armor Pen and some tank. Because of the strength and potential in her kit, she excels in trades. She can also spam these abilities because of her lack of a restrictive resource. Her AoE is amazing for waveclear and her dueling with engage and disengage is godly.

But. She has limits. She can be incredibly outplayed. She is kited with ranged and especially CC. But her real weakness lies in the fact that she HAS to go all in to do anything. Her kit rewards canceling (passive and Q/E-cancelling), which often leaves Riven players defenseless after a trade or even when farming. Most Riven players want to use their shield as an engage, but remember this is her only true defensive ability. Sure, Q can be used to dodge and W can be used to disengage, but utilizing proper positioning and baiting/kiting out her Q or E can leave her unable to reliably dodge or shield poke. She suffers against sustainable enemies, namely Garen or Renekton. She can chunk you while you are CCed from W and Q^3, but afterwards she must walk away.

Because of her kill-you-while-I-CC-you-with-my-QWER playstyle, if you simply don't try to fight her when she wants, you win because she needs that early lane pressure or even a kill to stomp your team into the late game.

Nasus, for instance, is often thought of as a easy matchup for Riven because he can't fight her without getting bursted. But if he just stays at tower, farms his Q or pokes with E, it becomes a very sad lane for Riven, who gets outscaled by Nasus while he sustains any poke using his passive.

TL;DR: Once she uses her abilities, which are often used in conjunction of each other, she has nothing. Also, she requires early game dominance to be able to be powerful; if you can poke/sustain/kite, you made her early game a nightmare, therefore making the rest of her game a nightmare. Play safe early if you must, and keep up in CS. You can easily win lane against a Riven, and most other AD casters, with this playstyle.

TL;DR the TL;DR: Play safe, CS, and use positioning to go in at opportune times when she's all out of juice.