As cassiopeia, Avoid getting hit by her Q in this matchup. You will be taking a lot of damage otherwise which will force you to waste your W.

Always try to CC her when possible. Once CC'd, she is quite open to all-ins from your end.

Do not go close to her even if you land your Ultimate R on her. She can easily turn on you with her Ultimate R if you're not careful.

Keep the wave in the middle of the lane and try to expose Cassiopeia to ganks as much as you can. As cassiopeia, Avoid being struck by his Q in this matchup. You will take a lot of damage otherwise that will force you to waste your W. Always try CC when it's possible. Once CC'd, it is open enough to the all-in of your end. Do not approach it even if you land your Ultimate R on it. It can easily light you up with its Ultimate R if you're not careful. Keep the wave in the middle of the way and try to expose Cassiopeia to ganks as much as you can.