This guide is how I perceive playing Riven. There are two ways in my opinion to play this champion, based on what the other team is doing. I find it this champion is easiest to play with flat damage, CDR and defensive items.

You are not a carry, such as vayne, stacking crit, AS, and AD.

Disclaimer: This is how I play the champion and has led many successful victories. No I have not been high on KDR, but I have gotten first blood and end game, can tank very very well. Also, this is my first actual guide on here, so comments are welcome on how you all play this champion.

Pros

Great harass
Great laning
Great farming

Cons

Weak vs ranged AD/AP
Squishy without defensive items
Need to make many b trips

I use 21-9-0 for my masteries, to give myself survivability and damage early game. This can be your preference, though out of many games since this champion has been out, I have found this to give the most presence during laning/farming early game.

Runes are simple: I take flat armor pen marks, flat magic resist, flat health, and armor pen quintessences.

I use these items to prioritize my early game.

I start with broken wings, then move into valor and qi burst. I almost always max broken wings first, then valor, then qi burst. I change my sequence if I feel valor will benefit me more than qi burst or broken wings.

qi burst when 5-6 minions are in range, broken wings, auto attack, broken wings, auto attack, broken wings. Easy to farm with this champion.

If you lane is being pushed and you cannot stop it, jungle for a bit to allow them to over extend and then move in behind them, exhaust, flash, valor, use everything to drop them and force them to B.

Early Game

As stated before, CDR, AD and survivability is what I choose. I almost always start with a dorans blade, then move into boots and health pots. From there, if my laning is fine and can harass fine, I grab another dorans blade and move into wriggle's lantern and boots of lucidity. Make sure to use your vision ward the lantern gives you wisely.

Mid Game

Normally, I start to prioritize surviving now. I grab magic resist or armor items and move into force of nature or thornmail first depending on my lane.

End Game

Picking up a blood thirster

I use exhaust and flash. Great for chasing down enemies and also running. These are a must in this build.

Overall, prioritize items that will give you the best harass and laning/farming presence. If you are facing an AP, you might want to get the negatron cloak early or facing AD, grab the chain vest first, before boots of lucidity.

As stated before, I feel this champion not being a carry, and only benefiting from CDR and AD items, there just are not enough of purely these to stack only these items.

The champion shines when you can tank 5 players while your team sits back and nukes.

Final thought

Finally, you can skip defensive items and go straight AD if you are fed heavily, but you will still need these other items late/end game. Eventually you need some of the defensive items, or you'll be nuked in your first valor, broken wings, qi burst, broken wings combo.