Zed is a champ that rewards fast thinking as well as positioning. Quick reaction times can help a lot.
Also, Zed's ult does little damage on its own. What you want to do is save as much damage potential as you can for your ult because the damage from the "pop" depends on how much damage you put in while the ult is active. This means... you can have three Qs going off (from you, your W shadow, and your R shadow), and your Es, and any basic attacks you can get off, and maybe BotRK active, R back to your shadow when you need the safety and POP! Also figuring out when your damage is enough for the ult to kill is a skill to master in itself.
I'm no master but that's what I've picked up.
I'd recommend looking up Azoh's "Zed School" as well, for Zed practice.
EDIT: Even if this doesn't help your own Zed'ing. This might help you immensely when laning against a Zed, getting to recognize his poke patterns, his CDs, his most successful playstyle so you can then exploit it and keep yourself safe.