*Tips for zag in general*
Turn Q to QUICK CAST (not on release) q on release is just clunky, regular q is clunky, but quick cast q is amazing. it just fires in the direction of your mouse cursor
Turn W and E and R to QUICK CAST ON RELEASE. Having the others on release helps land the skill shots and makes sure you don't waste your abilities
Put creep down constantly. You should never have more than 2 charges of creep.

Level 1

Corpse Feeders (E)
*If teamfights will primarily happen away from lane, take the E talent

Infest
*If teamfights will primarily happen in lane w/ minions, or you're solo laning, infest
-Infest is slept on. Gives major dmg boost to archer minions, pushing waves hard, and when you clear enemy waves, your boosted minions will focus heroes. Don't underestimate this

Level 4

Medusa Blades (Aoe Auto Attacks)

-I take this the majority of the time. It can really help vs enemy healers who are mostly single target.
It helps clear camps, and just adds more poke dmg to zag's already insane poke

Envenom
-I started taking this situationally and I love the results. Especially vs like tracer or a squishy hero. It does a BIG DoT, enemies don't expect it.

Level 7

Viscous Acid (Slow on Q)
-It might not seem like much, but this slow can save your life, it can save your teammates life, it can secure a kill bypreventing an escape, etc.
I usually take this

Bile Drop (Quest on E)
-This is very feast or famine. You get a baseline size increase to the drop, but if you don't hit 12 heroes, it doesn't do anything else.
This does MAJOR MAJOR DPS increase post-16, if you complete it.
I take this talent when I'm confident I'll complete it, or when the enemies are very very beefy, or if we already have cc and don't need the slow

Level 10

Maw
-This is just my personal preference. I always go maw, 100% of the time.
Landing maws is easy after you've applied a slow to the enemy team.
Make sure your heroic is set to QUICK CAST ON RELEASE
Hold your key while you aim the maw and then place it where you think the enemies will be walking (theres a slight delay)

You can use maw to bodyblock, save your life, or secure kills.

I recommend using TRY MODE to practice maws over and over until youre very comfortable.

Try to always get 2+ people in a maw unless you're guaranteed a kill with the 1.

Nydus
-There is a case for nydus, its just not my taste.

Level 13

Hydralisk Transfusion (Heal on W)
This is usually the go-to, when you send your W out on a HERO, you get constant health regen.

Protective Coating (Armor on Creep)
I take this when the enemies can't easily clear my creep. 20% dmg reduction while on creep is insane.
If enemies clear creep fast, this talent is useless tho

Level 16 (MAJOR GAME-CHANGING POWERSPIKE)

Corrosive Saliva (% dmg on W and E)
I ALWAYS take this talent. Throw out a W, drop an E, and if all your minions successfully land their attacks, you take out 58% of the enemies max health, no matter who they are.
The minions move faster on creep, so they can chase enemies down easily if creep is down.
You can send out your W and E on the enemy tank to quickly force him to retreat, but the combo is fine to drop on anybody.
Try to send out your W on an enemy who can't easily kill it (like valla can)


Level 20
Pack Instinct (All dmg increased to enemies affected by W)
This is just a big dps increase to all sources of damage, autos, minions, envenom talent, etc, to anything you use W on.
I believe it even works on buildings. Buildings will melt after sending out a W and throwing some Qs on it