Hi! Velkoz being my favorite champion, here is a guide on how to play him mid.

Passive

Each of Vel'Koz's damaging abilities apply a stack of Organic Deconstruction Deconstruction to enemy units for 7 seconds, up to a maximum of 3 stacks. Upon reaching 3 stacks, they will detonate, dealing true damage to the enemy unit.

Q

Vel'Koz fires an energy bolt that deals magic damage and Slow icon slows the first enemy hit by 70% for a few seconds. The Slow icon slow decays over its duration. After a brief delay, Vel'Koz can activate Plasma Fission again. Max this last.

W

Vel'Koz's W (Void Rift) is a skillshot that is intargetable and cannont be blocked. It opens a rift in the earth that deals damage immediately plus after 0.25 seconds. It can stack up to 2 times, so using this to harass your enemy is optimal. Max this first.

E

Vel'Koz hurls an anomaly at the target location. When it lands, it collapses, dealing magic damage and Stun icon suspending enemies hit for 0.75 seconds. Enemies close to Vel'Koz at the time of impact are also slightly Airborne icon knocked back. Max this second.

R

Vel'Koz Root icon roots himself in place and projects an energy beam in a line for 2.5 seconds, dealing magic damage to enemies caught in its wake in 0.25 second intervals and Slow icon slowing them by 20% for 1 second. Take this at 6,11, and 16

Trading with Vel'Koz can be tricky, but here are a couple tips to increase your chance of trading with the enemy laner.

Poking

Vel'Koz's W (Void Rift) is a skillshot that is intargetable and cannont be blocked. It opens a rift in the earth that deals damage immediately plus after 0.25 seconds. It can stack up to 2 times, so using this to harass your enemy is optimal. It is also your best waveclear.

Getting CS on Vel'Koz is like getting CS on Azir. Your auto attacks deal damage almost immediately you right click something. Mastering this will make you a better Vel'Koz and a better Azir player.