Well I mained Zed and these seems to be the most effective. No need for a massive explanation.

Well Zed is a better mid champion, being able to do the most damage hitting the champion with the Q b4 anything else. While Zed is amazing bot, any thresh would counter him quite easily, and if there is and Ashe, you're done. Usually you face a Katrina, meaning when she ults, you ult. When you ult you have a period where you take no damage. The further you're away from Kat and cast your ult, the better. A longer teleport time meaning you take less damage. Stun screw Zed so if you're facing Stuns, get the magic resist boots. Zed is good for his contempt for the weak and it makes Assassinating easy. Use it often. Your E has the shortest cool down, if you would like to Cool down to reduce, feel free to.