Playing Kassadin midlane is very hard and tough especially when you get countered, with for example AD Champs / AD Ranged Champs. It's beneficial to have good mental as a Kassadin player.

Help your jungler with placing a ward into the deep jungle of the enemy, with that you help your jungler to locate the enemy jungler and his pathing, with that your team can play safe and more aggressive when they know, where the enemy jungler will path.

There's a big difference aswell if you are laning vs a champion who is ranged and a champion who isn't. For instance if you lane vs an AD champ that is ranged you will barely keep up with maintaining good csing since he will pressure you even under the tower. You have to keep farming with your Q and play safe and wait for your jungler, a good mental and patience is the key here.

When you are vs Melee Champ, doesn't matter if it's AP or AD it's beneficial to know when to take the trade and when to give up cs for it. You are always looking to proc your Electrocute in these matchups with for example Q Autoattack W.

In the early game it's really hard as Kassa to have the pressure in lane especially if you get countered, so it's good if you ping your Jungler that you cannot contest the scuttle/crab.