Fizz is a good champion for ganks. If you will gank bottom and there's a support champion in enemy team, no need to use grass to hide because you know; supports use wards to illumine nearby grasses. Directly attack after waiting your 2 bottom teammates. If there's not a support, that's a chance. Because you can hide in grass and wait for a right ultimate. And here comes the right combo:
R-Ultimate(Chum The Waters)-> Activate W(Seastone Trident)-> Q(Urchin Strike)
After that if your hp decreased so much or your teammates gonna die, use E (Playful/Trickster) to escape. But ıf you still has high/middle hp, you can use Trickster active skill to hit enemy again.

Fizz doesn't need much movement speed in the beginning because of Playful/Trickster. In mid lane, you can dodge your AP carry enemy easily. Especially if you have a blue buff. In earliest game (at least until being level 6), just farm; hit creeps' last health. After being level 6, you can use the same combo [R(Ultimate)-> Q(Urchin Strike)-> W(Seastone Trident-> E(Playful/Trickster)-> Ignite (If necessary)] to burst, in fact to gain even a first blood ! As I said, you can use your Playful/Trickster to escape if you have low hp, that's simple because of your untargetablity.

Pros:
-Easy and high burst
-Easy to escape from sudden ganks
-Having a serial combo
-Easy farm

Cons:
-Squishy
-Low mana in the earliest game