I'm kind of a Zilean main. Here is what ive been doing.
-What I've been doing is Maxing R>E>Q>W.
-Slow them down with E than Q-W-Q them for a easy stun.
-If you are being jumped on and your all alone Q-W-Q On your self. stunning everyone around. Trying to Q-W-Q anything else is really REALLY risky. and since you don't do damage, just become a mini amumu is better.
-During team fights, use the ult on your carry(the one whos being focused) this isn't the greatest but it wards off things like Ekko, talon, LB anyone who can one shot your carry and they can play like idiots.
-Speed your self, hit W slow them down. This is a great way to engage but It can leave you in a awkward spot if you go to far.
-Don't ult your self if you can ult anyone else.... like anyone..... Don't waste your ult for the first 2 ranks on your self.)
-I like to build ROA, before 20min, but if I can't Build Righteous glory.(Usally the righteous glory is the best option)
-Q-W-Q in a safe place in the lane so you don't take farm. (Some times you don't even want the stun, just use it to zone them) but....
-I actually reccomend not getting the Spellthief's Edge and instead get the Relic Shield incase you can't help but Q-w-Q on creeps to get the stun(this way you can safely give cash to your carry)
-Build Max Cdr, You're basically a walking Ga for everyone.
-Also build Tanky rather than Damage, this way people can't pop you and you can ult the.... not tanky people.
-Ward
-Upgrade trinkets.
-Build banner of command and/or Zz'Rot Portal. (this to help push waves)
-Don't leave your carry.
-I personally like grabing TP so I can Tp to ult.
-I build mad damage if I'm with a friend and twitch(Put a bomb on him, speed his ass up, he goes invisible and he goes next to em, and pOP)