Riven's Broken Wings locks onto the champion your cursor is over at the time of cast. If you want to move past your opponent, make sure that your cursor is past your opponent as well.
Riven lacks a source of healing or strong defense and must compensate with burst combos. Lead into fights with Broken Wings and Ki Burst, while using Valor to escape and absorb counter-harass.
Riven has a great deal of mobility but she cannot move very far with any one skill. Rooting or silencing her during her combo will greatly reduce her effectiveness.
All of Riven's damage is physical, prioritize high Armor if an opposing Riven gets out of control.
Riven excels at dueling multiple melee attackers at once, as she will be on an almost equal footing damage-wise. If pairing up against Riven, don't go in as double melee until she has expended her full combo.