Riven is an early game dominant champion who can take over the map through short trades. Try not to trade with her unless you can match her trading potential.
Riven will often play hyper aggressive and try to outplay you. If possible, try to bait out her main abilities and then re-engage when she has cooldowns. This is your best bet when laning against a Riven.
Keep the minion wave frozen near your Tower. If you are playing close to your Tower, her all in potential is limited as the Tower will protect you and she will not be able to look for frequent trades.
Riven will look to split push during the mid game and apply pressure to the side of the map. Send a player to stop her from pushing and taking objectives. If you cannot fight her- send 2 champions or just clear the waves.
Teamfights can be difficult for Riven as she is prone to kite. If she runs directly towards you, kite her away and poke her down. If you can get her low, she will have to back off which will give you a chance to re-engage.
If Riven is smart, she will not run directly at you to team fight. Instead, she will play around fog of war and attack from the flank. Try to ward your flanks to prevent her from achieving this. Additionally, do not stick too close together so she is unable to take everyone down at once.
Riven can easily 1v1 any champion at level 3 if she is in a favourable matchup. Do not over extend to reduce her chances of killing you.
Riven’s level 6 power spike is pretty potent. Opt for early armor to protect yourself from all ins.
Once Riven has completed two or three items, she becomes very strong and will be able to take down any squishy or any champion that is not a tank. If you see her running towards you- just back away.