Zac is a tanky damage dealer with great mobility. His damage is pretty high and his sustain aswell, he is good at getting last hits as you can spam your abilities, and he also get healed when spamming spells because he gain 4% of maximum health when he pick up his slime while his abilities cost 4% of current health.

Open up with Elastic slingshot and immediately cast unstable matter when you land and follow up with stretching strike and auto attack, then just spam your abilities. When you use your ultimate, make sure to keep spaming unstable matter. And also when you use your ultimate, keep in mind that you don't bounce in a very high speed, so don't use it at too far range as I did in the beginning. You will probably not catch up with your enemy.

You should start at red buff --> wraiths --> wolves --> blue buff --> the 2 golems --> wraiths..

The items I have picked is a combination of damage and great sustain, with this build you can survive pretty much damage, aswell as you can deal alot.

The masteries is aswell a combination to get as much health as possible, and also get some damage bonus.

Runes:
Magic Pen. marks for some extra damage.
Magic Res. glyphs for some survivability against Magic damage dealers.
Scaling health seals for some extra health, as it's your resource for abilities aswell as it gives you more sustain.
Ability Power Quints for some extra damage.