I've been featured several times, so it's kind of an interesting one to answer...
The first time, it was a surprise. I'd just been put forwards for a "community feature" here on the forums, which was something Tapas were trialling at the time, and so I was like "YES! Finally! I will get some sort of feature!" having been updating nearly a year and clawed my way up to around 275 subs without one... and so I was waiting excited for my community pick to happen in the next few weeks... and then immediately got a staff pick, so I was sort of blindsided by it!
Nearly every feature I've ever had has boosted my numbers at least a bit. The most effective ones tend to be anything higher up the page, so my very first staff pick back in 2020 boosted me from around 275 to just a smidge over 500 subs. The least effective feature I've ever had was a little while after that, I got featured in collection called "Adventure!" which was right at the bottom of the page, and everything else in there was a premium comic. At the time, I hadn't really thought that much about my thumbnail, and some Tapas features were still using thumbnails not covers, so I was like... right at the bottom of the page and looked kind of crappy compared to the rest of the group and only got maybe 10-15 subs off it... it was a learning experience! 
Another good one was of course being on the "Feed" and more recently community banner features. Tapas emailed me asking for a banner for that and a tagline, and while it was maybe only roughly as effective as any other feature, there's something kind of special about seeing your banner up there.
I've also been in the Pride collection, which is better for subs than I expected, and the Tapas easter egg hunt, which is terrible for subs, but good for views 
In terms of tips, the big one is presentation and looking like your comic/novel would look like it belongs in a group with other, more popular Tapas comics or novels in a similar genre.
So in my case, I think a big reason Errant gets regular features is that the cover, artstyle and palette look like they belong in a group with other action/adventure/fantasy focused LGBTQ+ titles like Pandora's Devils, Hard Lacquer and Alien Heart. Tapas likes to feature those comics, so it's easy to throw in Errant too to round out the group, and there's strong readership crossover between them.
A professional looking title font and a bold, polished cover will get you a long way. For novelists especially, I'd urge them to get an illustrated cover in a style that matches premium or popular titles well, this has paid off so much for titles like "The Saintess and Villainess". If you have friends with design experience, get some advice! If your cover, banner and blurb are things you just threw together because you wanted to focus on just making pages or writing chapters, that's something you'll want to fix if you're looking to get a feature.