Early game the only real thing you want to do is FARMING and you also want to be careful for ganks ( one of zeus big weakness is 0 mobility, if you play vs good ganker you might have a hard game)
CS with your Q while also auto attacking with to be sure you won't get denyed.
get a soul ring to never run out of mana while buying some clariy potion here and here to be able to get every cs with your q ( you won't get much with your auto attack, since if you went soul ring you won't have much extra intel your auto attack will be almost useless)
Once you hit your level 6 you def have kill potential for both the mid lane if you have someone that can help you or top or bot lane. With a full mana bar with 5 Q in a row you will do insane dmg on a lvl 3-4 support or carry with your ultimate to finish them.
Get mana boots and bottle after soul ring and you should be able to clear waves with 3Q.( try to get one auto attack on the range creep it can stay alive early with only 1 point in E) Will need 2 q to kill the range creep.
after you clear the waves, you can, wait for the other wave to come or try to get a gank if you see good Opportunities.
You will start getting more points in your w which does INSANE damage (and also cancel out TP and give vision in night which also auto attack someone if you hit it on the ground)
You have a lot of items Opportunities, it depends on game but bloodstone is always a top item choice.
Zeus without mana is the most useless hero in the game ( his auto attack has no damage and range, all his abilities that does dmg cost mana, .)
after that or BEFORE that eul scepter is also good to be able to live vs things like SF ultimate, invoker combo and can also use it offensively to help set up a good combo from your team.
Aghanim is the second best item next to bloodstone for zeus, can cancel out tp from ANYWHERE, insane dmg combo with your q+w+r combo. Get that item quickly.
Keep clearing waves quick and always have tp on you so you can help your off lane or safe lane if they get in trouble ( once you are lvl 6 it's always dangerous to do something vs a zeus... his q-w-r combo is almost always a one shot if they don't have any magic resist or rain drop to counter your crazy burst)You can also start jungling if you have your bloodstone since now you have very good mana regen AND health regen to be able to tank some hits if you fail your jungle kitting, the health regen will also heal up the soul ring dmg)
Zeus keep getting better and better as the game goes on...
With the mana regen from bloodstone and eul scepter you will be able to spam your Q to farm jungle and everything non stop so you will keep getting items easy.
With the mana regen you will also be able to never run out of mana in fight ( if you still do, try to always have clarity potion on yourself)The constant damage from your Q spam and the INSANE damage coming out of your W will be no fun for your opponent. Add the passive which wreck anyone( even tank ) through the game and you will see why Zeus is one of the best mid if not the best in my opinion in the right hands.
Once you are lvl 25 with octarine you will even be able to clear mega creeps easy, also will be able to def the highground from far( very hard to push highground vs zeus even without his lvl 25 q damage.)
Always stay in the background, sometimes you can try to make plays by yourself if you have a blink dagger and aghanim, your aghanim + ulti + W + q combo can literally 100% to 0 % anyone that isnt careful and don't have any magic resist.
Max Q then W ( one point in your passive at lvl 2 or 4 depending if you need your w to cancel out a tp very early level )
Maxing Q make you able to farm the creeps without anyone being able to deny you ( only TA can do that cause her auto attack are just better than your q, she's like the best hero to play vs zeus)
XP at level 10 is always the best talent imo. Zeus with level mean more damage and more burst which is always good.
Level 15 one should be move speed, zeus weakness is his bad mobility so the move speed is seriously nice to take which add up a nice movement speed to eul scepter and travel boots.
lvl 20 is seriously a hard choice some games, i rlly like the Cooldown reduction added up to octarine you have insane CDR for both your aghanim w and ultimate, but i also like the stun on W since if someone stay in your aghanim + you use your w on them you can almost STUNLOCK them hard, good vs hero that have to run away like void, storm, etc ( also people can never blink out of your aghanim since the damage is always instant once they are out of their eul scepter, the damage from the aghanim ability will always be faster than the blink reset.
Level 25 should always be the Q damage... that talent is just insane.
Make you able to clear wave insane fast ( can even clear mega creeps late game.) also crazy insane damage in long fights.