Riven is my best AD midlaner and you can play both full ad or offtank. I dont like full tank riven so much because you have to deal too much damage with your burst.

Pros:
Great early laning
No mana(spamming abilities)
Mobile champ with Q and E
Good CC (knockup stun)

Cons:
Cannot harass
Damage is not huge early game
She needs to reach someone in order to damage him
Ult is not hard to miss

In teamfights hold on to your shield until you actually need it. Try to stun as many people as you can while making sure your Ulti will hit all of them.