I would firstly suggest finding another person, or preferably 3 other people to play online with, so that you can practice in matches with less stress. Really just any practice is good, I have played Custom E-Liter and have 500k ink with it, and it is about 1/2 solo, 1/2 team with the weapon. You should definitely use the practice room to practice horizontal and vertical snaps, and jump shots. You can also use the ramp for peek shots.
Before using Custom E-Liter I used Kelp Scope a lot, so maybe practice using the shorter charges, then transition to longer range if you want. Really find whatever charger you want to use, or like to use. Then start with turf war, then transition to ranked. You could even make an alt account, I did that, and got to S+ using only chargers, which really only took me ~12 hours. These kind of challenges are really helpful, even if it takes you weeks/months to get to your current rank, you will gain a lot of knowledge on the weapons.
I find the more I play the more things like snapping shots, or peeking seems to come naturally, so I can mainly just suggest that you get a lot of experience over anything else. There is no magic way to get better at charger, but watching other good chargers can be extremely helpful. I am considering doing charger/splatling training sessions with people this summer, since many people seem to want help with these weapons, and I know a lot about good technique, and seeing people's small errors, maybe doing like a "zero to hero" kind of thing.