the cover plays a huge part for sure. next is the plot line and the art. then, other reader's reviews. sometimes when I really liked the cover and summary, I refrain from reading reviews cuz it might ruin the experience.
(tho most of the times, I just reread stories I've read before when I remember about them)
sometimes if i see some manga with where the cover is too goood then i'd read that . otherwise I open one of my favourite mangas and go through reading lists which have that manga and then I add a shit ton of mangas from the reading lists to my want to read .. it's like a never ending loop (2 years now ) of just going to reading lists of mangas that I like and adding more to my want to read.
do u just pick up the first thing that pops up on your page or do u go for specific tropes or authors?