With fizz you should try to first farm without engaging until level 3. when you reach it you should use q to poke your enemy, inflicting the passive from the w, which allows you to get down plenty of life. After poking you can just return unharmed with playful (e). When you reach level 6 poke him till he has a bit more than half health, then go at him with q, then ultimate ability then playful and obviously activating w at the beginning. Also throw him ignite, just in case. If he hits more than expected you can use barrier too. If you cant kill your opponent then gank, fizz is assassin so you should always aim to kill the persons that go too far away from turret. In team fights be careful because you are squishy, and your death is the cool down. You should aim to rush in and out of team fights, and avoid dieing that way