Hey guys! This is my first MOBAfire guide, so be nice ;).
I have been playing alot of Riven recently, and I've been quite succesful!
As of now, I don't have the required time to make a whole guide, so for now I'm just going to give you some parts of it. I will finish it whenever I have time.
If you want any in-depth guide with Riven, there are many guides out there!

Also, please read the whole guide before voting.

Here is a guide that I recommend if you do not find my guide useful at its current state.

BlueInSane's Riven Guide

This is what separates the good and bad Riven's. Always use your passive after an ability in a fight, otherwise you won't be much of a threat to the enemy team.

Most new players will just mash Broken Wings and afterwards complain about how little damage it does. As I said above, always use your passive in between your abilites, otherwise you won't do much damage.

This is your stun. Most Riven players will know that this stun, has a very short range. You need to get toe-to-toe with your enemy before you can use this and hit it, remember this.

This is a small gap closer, aswell as a shield! This will save you from some harassment, and will allow you to harass and come out unharmed in most situations.

Ah. Your ulti. Always use this in the beginning of a fight! This will allow you to get more range on all of your abilites and 20% extra AD!!! This is a huge amount of damage.
This also allows you to use Wind Slash. Use this in every fight that you have your ulti activated in! It does more damage the lower the targets health is, so use this at the end of the fight.

Pros:

+ Fun to play
+ High mobility
+ Doesn't use any source (Mana, energy etc.)
+ Has a stun that can interrupt channeling abilites!
+ Awesome Ulti!

Cons:

- Squishy early game
- Can be hard to play
- Very short ranged stun

Many of you might wonder why I max Broken Wings first.
It's because it gives you the most total damage! Sure it doesn't have the highest AD Ratio, but it can be used 3 times. Now this gives you great damageif mixed with Runic Blade!

Sure you can max Ki Burst first, it gives you less CD on it, and a little bit more damage. It has a decent AD Ratio aswell, but you can only use it every so often.
So Broken Wings is better IMO. You can mix up the skill sequence how ever you want, this is just my personal playstyle, so please don't downvote this guide just because you don't like my skill setup.

I get Doran's Blade whenever I don't go top solo, because of the +100HP and +10AD.

As for the boots, I get Ionian Boots of Lucidity, since you need as much CDR as possible for Riven, since her abilites have a decent CD.

I get a Phage to counter some of Riven's squishieness early game.

I get an Infinity Edge aswell, for the sustained damage output.

I build a Bloodthirster after my Infinity Edge just because it's too risky for me early-mid game to grab a bloodthirster before my Infinity Edge. "Why?" You may ask. Well, it's because you lose all of your Thirster stacks whenever you die. And since you are still kind of squishy, and easy to kill when focused, it's not worth the Bloodthirster before the IE IMO.

The Frozen Mallet. Now this, this is what makes up for Riven's squishieness! By now you should either be fed or just simply hard to kill.

After your mallet the defensive items are situational!!! Don't downvote the guide simply because my defensive item's doesn't counter your enemy team!

I also get my Hexdrinker. This is just if they have any AP's on the enemy team, that usually kills me or just hurts alot. It works wonders on Riven since it gives u AD aswell. But don't use this if the enemy team is stupid enough to go with only AD champs. (Rarely happens, but it does happen every now and then.) If they do go all AD, just build something else, what you build is up to you.

Thornmail is by far my favorite defensive item in LoL, if they got any good AD's on their team. It is just.. awesome! Of course you won't be using this if they all went with AP's (Also, rarely happens), if they do it's up to you what you build.

This is just my personal rune page.

I find that the extra Armor pen from Greater Mark of Desolation is very helpful through out the whole game. Armor pen will help you more than pure AD runes will, so I recommend using Armor penen not AD runes.

As for the Greater Seal of Armor, Riven is very squishy early game, and she needs that extra armor boost.

I take Greater Glyph of Cooldown Reduction aswell, since Riven isn't an auto attack champion most of the time.
She depends on her cooldowns, so I recommend getting CDR.