I keep missing abilities

[Leetard]

Hi. I'm a 1650 mmr player, been playing hon for quite a while.

I've notice I tend to miss my stuns alot of the time... even when its easy ones as witch slayer or magmus.

Is there anything I can do to help stop?

[[E]Clytemnestra]

learn their ranges(ws stun is targetable)

[[eNHa]Myzreal]

Well the reason for that maybe be either low FPS which makes the game choppy, bad mouse or a lack of concentration.

In case of low FPS you need either a better machine or you could try lowering the details. In case of the mouse you might wanna get one with higher DPI or just try to clean up the existing one. In case of lack of concentration you just need to focus more :P

[Sherwood]

Players who can see you on their screen will tend to be quicker in reacting to you "going about to stun". It's a subconscious thing players develope.
Try stunning from the shadows. The window of reacting is smaller then.

On the lane if I'm against competant players, and I stun from the lane, it's pretty much impossible to land a stun.

Portal Key helps with disability with target area spells.

[[xBM]Ackwell1]

You have to learn how to read ppl in just a few minutes. Some heroes especially mid can kill theyre opponent very early with well placed skillshot and you need to be able to read your opponent by just laning against him for a few minutes. Usually against "bad" ppl who can recognize your animation etc will most likely try to run into tower so aim it a bit behind of them.

[Jenova26]

I used to miss hooks with Gauntlet ALWAYS. So, I started playing him in MidWars. Now my hooks are pretty damn good. Same thing with Valk and chucking Javelins. Take the hero you're struggling with and queue a couple MW games. Even one game of constantly throwing stuns with one hero will significantly improve your skill with them.

Or you could load a practice game and just stun around constantly, but that will teach you nothing about reacting to your opponents.

[supply_depot]

Players who can see you on their screen will tend to be quicker in reacting to you "going about to stun". It's a subconscious thing players develope.
Try stunning from the shadows. The window of reacting is smaller then.

On the lane if I'm against competant players, and I stun from the lane, it's pretty much impossible to land a stun.

Portal Key helps with disability with target area spells.

This is good advice. Players will recognize when they are against a stunner, and be preparing to juke stuns at any second. Being less predictable is half the battle.

Also, on some heroes (you mentioned Magmus and Witch Slayer), you can target heroes with stuns. This is at your discretion, sometimes you want to ground target stuns to hit multiple people, but other times you need guaranteed accuracy on a specific hero. Both Mag and WS can target a hero specifically and guarantee a stun (unless it's disjointed or you lose sight of them in shadows).

Finally, practice makes perfect. Every hero's timing is a little different and it requires some muscle memory.