Cassiopeia Counter Tips
Predict the timing she is about to cast her ultimate, turn around and avoid getting stunned. This will greatly increase your chances for winning the duel.
If you dodge her poisons, after casting the first E(Twin Fang), it goes on high cooldown and without it she is basically useless
Starting with a boots will greatly increase your chances of dodging her Q most of the time which should also help you take the first blood bounty.