Hmm, there are several things that attract me to a comic ...
An interesting, cool art style will make me click on a thumbnail. I've found many great stories because I liked the art style. That is, of course, entirely subjective. Quality, which is somewhat objective, does matter to a degree, but the art definitely doesn't have to be perfect. As an artist, I really enjoy watching other artists grow and learn (and tbh my own comic chronicles my own growth and learning process even though the story isn't about that at all XD). For the most part it's about whether I like the style, which is a matter of taste. Personally, I prefer either realistic (not too prettified) or just unusual styles that stand out, but that's not a hard rule. There are always exceptions. Sometimes my brain just goes "I wanna read that!".
It's similar for the content, I enjoy a wide variety of genres. There are some things that will definitely keep me interested (positive polyamorous, aspec and arospec representation, unique/unusual relationship structures, subversion and deconstruction of certain tropes, but also angels and demons - at least if the demons are people and not soulless monsters -, mythology, historical settings and, yes, gay witches. Sorry not sorry, I love me some good old wlw witches) and some things that make me click away (pretty much every toxic romance trope, sexualisation of childlike characters, uncomfortable age and power imbalances, stories that are literally just about characters being toxic and 99% bitching and gossiping and deceit and everyone being shitty to each other because no thanks, I've been out of school for a while and I still don't miss that shit) and things that make me care about a story less (mononormativity, demonisation of all non-monogamy because no thanks, society already does that and I don't need my identity demonised in what I read in my free time), but besides that, pretty much any story can get me interested if I'm in the right mood for it.
Lastly, and I know that might seem unfair or controversial but I'm just being honest, yeah, if I had a nice interaction with a creator or we're even internet acquaintances or friends I'm more likely to give their comic a chance and read and enjoy it. Positive associations and all. I won't force myself to read something that's not for me, but I can't deny that there's a bit of a halo effect going on and I enjoy the stories of people I like more. That doesn't mean I only read my friends' comics though, I've never spoken to the vast majority of creators whose comics I'm subscribed to.