Luna is probably the easiest one: just get close. If you shoot first there is no way they survive. Even if you're surprised you might exchange. Basically it's a weapon very dangerous once it's in range. Don't get too close though, as someone kissing your face won't be hurt, unless you direct him. Lots of people like to put respawn on it as you'll get killed by trying to get in range, and stealth jump as it allows to get close and as I said, the weapon kills quite fast once you're near. But I would advice not to put too much, at least when you're learning it. This way you'll play smarter to get close, with stealth.
About range, it depends which one you're using probably. The vanilla is more support/defense oriented. The custom will allow you some power with the deadly splash and kraken. I didn't try much the grim, but it's probably in the middle, more flexible with the burst. The three weapons will need a bit or a lot of ink depending of your playstyle. I would say the custom is the easiest of the three, at least in solo mode.
About how to play it, first I advice you to go in the testing area. Look at your cursor (or whatever it's called, the little thing in the center of your screen). Shoot without jumping, shoot in early jump, shoot in late jump. This way you can see how much accuracy the weapon have. Train some direct shots, both at max range, that you need to know (it's actually a lot as the name implies), and very close. If you try to make several direct in a row, you'll understand how jumping can affect your shots.
Finally, the rapid series. You didn't talk about the pro so I guess we count them out. Anyway if you're not used to blasters, pro is probably not the best choice for now. First, understand that the rapid are way weaker. If you play it with no damage up (which is possible, as you can see in one of my most recent videos), you might have some opponent not dying from 4 or even 5 undirect shots sometimes (that's why people likes to pile up damage up on it, unlocking 1HKO possibilities). Again, you need to know the distance. If your opponent keep living too many shots, it means you're not at the good distance. Anyway, you need to make some directs here and there, so some training in the area may help too.
Finally, for any of these, make their strength shine. Basically, you're strong to kill people a bit hidden. Behind a corner, on high ground, on or behind the tower... Basically if you know more or less where is someone you have a way to kill him. But remember not to try too long, because you'll be a target if you take too much time.
Good luck. You can probably see some videos of blasters on my channel. Else, you can search on YouTube for KT Lee. It's a japanese custom range blaster, with lots of videos.
PS: I didn't vote. I don't know which one I prefer. I have max turf point on the custom range and it was my first real S+99 weapon, but I'm playing the rapid deco these days and quite like it. I guess I prefer having some range though I could like any of them, honestly.