As someone who's aim isn't fantastic but can still pull off some decent gameplay with the charger I'll say this, it's not always about hitting all your targets. A charger gets the kind of assist that doesn't even count in Splatoon 2, trapping and scaring away enemies so your team can take them out. That's if you don't make the shots first.
If you start out in turf it's good to pick a nice bit of high ground to control and ink all over, you can do that by crabwalking and just tap shotting, I find I end up inking my spot better than my Teammates. An example on starfish, I always head straight to the right, and cover all of that high platform just opposite the gratings to the right of the stage, and there's a good ink proof wall to stand on that gets you a nice view on the middle of the stage.
Only aiming tips I can give is snapping and shot leading, which everyone will already tell you. Takes a lot of practice but it works. You just have to imagine that player is you down there, and if you see a laser, you'll swim away, whereas if the laser is behind a wall and you can't see it, it's a lot harder to escape. I also find if I fire too soon I just miss and they get caught in my ink, if I give it an extra split second I can make the final minor adjustments to get the kill. Sometimes it's about compensating just the right amount, what that amount is, only you will realise after practice, but if you wait until the x appears on the crosshairs, unless you have absolutely amazing reaction time, you're probably going to be too late in getting the shot.
In regards to knowing when to stay and take the shot, it's all about confidence. If you think you can make the shot, then take it, it gets easier the closer they are as they're a bigger target, but if you think you're gonna miss, ink your escape and use your sub to your advantage, a splat bomb can really set someone back so you can get away and take another advantageous position.
Finally, if you want to main e liter, of highly recommend utilising your sub. Ink mines are no joke in this game and can be so useful. For example, the snipe in moray towers is a great place to sit, however now you can get flanked from about three different places at least, the most common being the wall to snipe and the right ramp leading up. I always leave a mine at the bottom of that ramp, mines now track whoevers detonated them, and should that miss, you'll still get a notification that your mine has gone off, meaning you can take heed of the warning and either aim down that ramp to your attacker or move away to another position. I generally place a second mine under my feet, if I'm not at snipe I can find out when the enemy team has moved up there and make my moves accordingly. Additionally, mines do 35 damage, meaning a partial shot, or two tap shots will kill. Use this to your advantage. These mine tactics also work great with the dynamo.
Finally, (until I think of anything else) a charger isn't about sitting still all game waiting for someone to come within your range. You push forward with your team, stay a reasonable distance behind them but enough that you can still pick off unnoticed flanks and anyone who gets your teammates first. A charger has to be the most map attentive player and has to know pretty much everything that's going on, and tunnel visioning into the one guy you keep missing is gonna spell disaster if someone comes from somewhere else.
Hope this helps anyway, I've never been that good with charger but I've put a lot of effort in, and have been able to reliably win games.
