1) Get invited to the in-game community features.
2) Log on and queue prime time (19:00 - 00:00).
3) Ask around, let people know you're queuing and looking to get pops. See how many there are on both sides.
4) If you feel like you've waited long enough, do something else, come back, or don't.
It's really that simple. Queue while questing or farming BoE epics etc. etc. There is so much gearing to be done in this patch, or gold to farm. If pops don't happen, then at least it's not time wasted completely.
This next section is aimed at EVERYONE, who thinks the 19's community is "toxic".
I've legit played so many different games out there (PvP-oriented). Dota, CS:GO, Overwatch (to name a few popular ones) etc. Without having played much League of Legends, I can't say that I've experienced the toxic community first-hand, but I think that legit EVERY gamer has heard stories of how toxic the League community is. Yet it's still one of the most popular games out there? So I ask you, do you think that WoW 19's is overly toxic? Have you played any other game / aspect that focuses on PvP? I can with CERTAINTY say that 19's is of NO DIFFERENCE to these games, if not even less toxic.
If someone calls you out in a rather heated moment (because that's what it usually is), you shouldn't take everything to heart. Instead, look at what the core essence of that message was. Reflect upon it, and if you really made a mistake, own up to it. Everyone makes mistakes here and there, and the ones that gets called out are usually the major ones. Ask for advice or elaboration after the games, join guilds etc. People tend to show respect if you show incentive to learn. Everyone is fully aware that people are on different skill levels. And if you "just don't care", then you shouldn't care about the comments getting thrown at you either.
Next section will be about bracket activity.
I feel like people who abandoned 19's for vet/f2p bracket weren't that involved or invested to begin with. If you cared enough, you'd be queuing like the rest of us (look at the top of this post if your argument is: "I can't sit in queue for hours"). And this is not meant to bash anyone. Everyone has different opinions on twinking, and what twinking provides for you as a player. It's EASY to notice all the Legion and early BFA twinks switching to vet/f2p bracket, because they didn't mind the leveler games and maybe found their enjoyment in sitting back and oneshotting plebs. That's how a lot of people started twinking back in the day anyways.
However, claiming that the lack of activity is due to the bracket being gate-kept by toxicity is a crazy argument, because that hasn't seemed to stop people from queuing in the endgame bracket, or other games entirely where the toxicity levels are, if not the same, then even worse.