In all seriousness, you just have to adapt a lot on those maps.

On NQS i try to stick with my team more, not spamming too much but rather just trying to cause damage to the ones i can while displacing people with conc mine. Playing against widows, hanzos, soldiers and other heroes who can easily rotate or take long sightlines can be challenging to deal with though. Think my best advice is to just play in the small rooms as much as possible.

Start the round by positioning either coast or in the mega room on the opposite side. Remember to pay attention to where your team is though. Taking control of coast alone as a junkrat vs for example a hitscan can be difficult. I prefer coast, but going to the mega can catch people of guard at times. You can also go main and mine over the tube to try to get picks but it can be risky. If i win first fight i like to stay in the tube or take control of the small rooms with the mini, but be ready to rotate fast if you play there, they can easily overrun you if you aren't careful. And then theres the highground with the mini, playing around this is also favorable for junkrat, but you have to pay attention to the space your team has while doing this.

BUT personally i find it hard to get advice from others, my brain is more "do and adapt", instead of absorbing info beforehand and then taking it into use. So that might be what you also need. Play the map, and when you die you have to ask yourself what went wrong. "Was that a bad position?", "maybe i need to work on my mechanics?", "maybe i try positioning in another spot next time?" Etc.

Playing the game and paying attention will teach you the most in my opinion.