I'm a new LOL player and its love at first sight with Riven. She looks like the female version of Cloud from FFVII. Anyway this guide is not about how best to play Riven, but how I play the Riven character. As many guide already had mentioned, the most difficult part in playing Riven is how to keep her alive, balancing between attack and staying alive.

After testing with some builds, I just don't like building a tanky Riven. Her ability does not allow her to hold tank very well.

Her plus point is mobility, and hence my guide is called "In and Out". Riven cannot stay at a point for too long, else she die. Hence, the main objective for this build is lane presence and harassment. Its more of a Support role, to constantly shave off enemy HP.
Don't scream KS at your teammate, because to Riven KS = Kill Secure.

I aim for the below in very game.
More than 5 kills (more than 10 would be nice)
Less than 5 deaths
More then 10 Assists

The defense runes is for me to survive the initial early game.
The armour penetration rune is obviously for offensive.

Again, the 6 points in Defence tree is for Magic Resist and Armour. More for the early game play. Everything else goes to offensive.

Only uncertainty I had now is choosing between Havoc and Vampirism.
Vampirism would make the early game slightly easier.

Exhaust and Flash, the most versatile spells in game.

Exhaust can be use for both offensive and defensive, and for both self and group.
If you think that an Exhaust can allow your team to finish off a well fed champ, use it.
If you think that an Exhaust can allow your team from an onslaught, resulting in many death on your team, use it.

Flash. To get away or to chase. Simple as that.

You can see that I select Valor as my first skill. This is very important to me because I wanted to take Doran's Blade as my first item. This is by far the best first skill/item combination with my skill level with Riven. Of course if you are confidient enough, you still can go with Broken Wing + Doran's Blade.

2nd skill will be Broken Wings and 3rd will be Ki.
Valor and Ki will be leveled togather.
Blade of Exile is level as and when available.
Broken Wings level last.

I guess this is one of the most interesting and debatable topic for any champion builds.
I would not say that my build is the best, but I think it suit the way I play.

The very first purchase is very important and the first ability comes hand in hand.
For me, after trying out different combination, I had chosen to start with Valor and Doran's Blade.

Boots are situational, be it Mercury's Treads, Berserker's Greaves or Ionian for CDR.

First item to build after that is The Bloodthirster. This item gives the the AD and LS to last longer in the field without coming back to base.

Next is IE. With this item, you see your damage goes up a huge jump.

Normally the game stop here, but if it carries on, I'll build the ghost blade. It compliment the AD, Critical chance and Armor penetration = more damage. If you need the added attack speed at times, turn on the active of the Ghostblade.

I've never went beyond this item.

1) Doran's Blade gives the added AD and HP. Valor provides the survivability passport in early game. Allow you to stay in game long enought to earn gold for next blade and boot.

2) Move, move and move. Riven combos is endless. In between always allow for an auto attack.
Q in, W, Q, Q, E out
E in, W, Q, Q, Q out
When doing Q, you Q at enemy champion on either 1st, 2nd or 3rd Q, depending on situation.

3) Use Q, W, E and Flash to run away or chase enemy champion.

4) Use E and Flash to get away from Uti and AoE.

5) Use E in, W, Qs (away from), Flash to support team mate to get away from enemy champion.

6) Don't do nothing, either kill creeps to earn gold or harass the enemy champion. If you are alone, be ready to run anytime.

7) Your objective is not to die. But having said that doesn't mean you chicken out. Sometime, you just have to be the one rushing in to draw out the enemy's spells on you.

8) You do not need to land all the 3 Q on the enemy champs. Use it as you see fit. One to go in, one to hit and one to get out.

9) All three abilities Q,W,E are your bread and butter. There isn't one that is better than another. Use in combination to confuse your enemy.

10) Blade of Exile (R), Needless to say, this skill compliment your basic Q,W,E. Use the second R as part of the combo, does not necessary be the finishing move.

I am not yet level 30 and had not got every runes to test out.
This build is far from complete and had many areas not tested out yet.

Thanks for reading. Have fun with Riven.