How would you do well in the laning fase when playing Kassadin before he becomes level 6? We all know that Kassadin is one of the strongest and most flexible champions after he hits level 6, but it's definitely a pain trying to get creepkills in earlier levels. Would you generally use your Q to last hit like Gangplanks Parley?
You can use general early game farming techniques, like walking back and forth on the edge of the enemies attack range. You can fake some moves so you can grab a few creepkills when not expected. Also, farming up with Q is indeed often used.
You can try and farm up a Tear of the Goddess as fast as you can, so you can spam your skills and use that to farm. Try to figure out per game if it is more profitable to use your spells on the enemy and force him to back out or miss some creepkills, or use them to get some creepkills.
Always try to melee lasthit the creep if you think you will survive and won't lose too many hitpoints. Else, just sit it out and farm under your tower untill level 6. Remember, two hits from a turret on a melee creep leaves him with so little hp that every champion can lasthit that creep.