I actually used to hate chargers, now I main them.
I was terrible at first (Of course) But I did improve a lot. Here's what I did, and sorry if it doesn't help.
Practice your aim in the testing area/Firing range/Whatever you want to call it.
I tried to practice my aim in the testing area in the original Splatoon once a day for at least 20 minutes. Of course, you don't need to do it everyday. Maybe like 2, 3 times a month. It's good to try to move around a lot while aiming. It makes you harder to hit, although it's hard to get used to.
Practice snapping (In turf wars, pbs, the testing area, etc)
It's good to practice quickly turning to an unsuspecting enemy to give them a heart attack.
But seriously, the laser pointer makes it quite obvious to see when you're being hunted by a charger, and a good way to avoid that is snapping. Apparently most people use the sticks to snap, but I just jerk the controller...
I don't recommend doing that. But hey, it works for me.
Choosing the right abilities for your charger.
This one is obvious. You can probably just look up Strategy guides for your charger and it'll tell you what that person thinks is best for that charger. Think smart, play smart.
Shoot, even when you know you're going to miss. (Turf wars, pbs, testing range)
You're going to miss eventually. Just get all the bad shots out of your system. It's hard to explain, but it works.
(For me at least)
Try playing weapons you don't normally play.
By playing the weapons you almost never play, you'll learn their strengths...And their weaknesses.
Sorry for the long comment, I hope this helps!