This genre is actually really easy for eastern authors to do because of their different style of storytelling. Rather than establishing an overarching plot that asks: 'How will they solve the conflict introduced at the beginning?', we are instead treated to answer of: 'What would happen if this scenario was to happen in a story?'.
There are two ways of introducing and using characters types of stories: Static Arcs and Positive Arcs. The rare slice of live using an overall Negative Arc being rare exceptions in this case.
What draws the reader into these kind of stories is the sheer difference between those who are going to be interacting. Those known as 'Flat Characters' who don't change may be ridiculed in other kinds of genres, but they work well in slice of life.
The whole reason it because people sometimes like seeing interesting characters interacting with each other. As long as there's a bit of intrigue and you know what your readers are looking for, even a character who doesn't change is highly looked on.
There are those who mix Positive Arcs (where the MC grows to become a better person) with a slice-of-life to create the barebones of a narrative. The beginning showing their flaw, the middle being what causes change, and the end being it.
However, for longer running stories, especially the ones that have hundreds of chapters, an interesting static arc is essential, as no one will care about a characters who aren't being consistent. In fact, their consistency is also good.
You don't see Luffy from One Piece changing much throughout his adventures, but what you DO see is others changing for him instead. Those who consistently stay the way they are no matter the odds seem to have an affect on other characters.
Though 'change' itself is a little bit overrated. Don't get too caught up in what a writer SHOULD do and focus instead on what you currently CAN do. The kind of character interactions you yourself find interesting is what will interest other people too.
If set in a fantasy world, make the rules bendable and allow people to have the chance to socialise with each other. There doesn't have to be an intended goal if the novel if wholesome.
For example: Even if you display a static father-son relationship with a good parent and son, no one will be able to criticise it if it brings joy to the hearts of the reader. Rather than a focus on events, this genre focuses more on characters themselves.
Though slice-of-life with a negative arc isn't to be looked down on for stories that are trying to run long in its genre. If people can change for the better and also stay the same, then it's only natural that there are those who change for the worse.
Just like a person's flaws, a negative change doesn't always have to be a bad thing. Though being short-tempered can devolve into wrongful violence, it can also change into a determination to do whatever the character is set out to do.
Just as the happy moments are part of our life, so are the serious moments where we make a change and strive for something. Everyday, tragedy also goes on the same way as a slice-of-life, and among those few, there are those that turn for the better.
Having a positive change arc somewhere after negative arc (even if you use a static arc to set things in) will have a gratifying effect on the reader as they see the characters they know and love overcome an emotional slump or hang up.
Though like I say, none of this is essential. As long as your characters are consistent and bounce off of each other well, you can make a great story. The things they do don't have to especially be 'talking' all the time as they are supposed to create ambience. Just like in real life, not everyone is talking 24/7 and are occasionally dead silent.
In these moments of silence is where the slice-of-life really shines. After all, the reason we love the straw-hat pirates in One Piece isn't only because of their interactions but how they mesh well together even in those moments of peacefulness.
Brook, that skeleton, plays the crew a melody in the times they are relaxing, allowing them to set the mood for their activities. Sanji cooks while the others are away and focuses on his recipes, while Luffy himself sleeps on their ship's mast.
Even when they aren't talking, characters are still doing something with their free time. They aren't simply made to talk to each other, but are their own fully established characters talking to one another.
It might be funny sometimes, it might be serious other times, they could also be curiously investigating something other times and sharing their opinions, yet they stay together. A good slice-of-life can also be used to show 'friendships'.
No one is good at everything, and we all need each other sometimes to fill out our flaws. There are those of us who can't exist independently. We seek out each other's company to talk to have a laugh or talk about are feelings, never forced to change.
If we are to change, then it would be the sake of someone else. As humans are irrational creatures that can't even hope to do positive things for their own benefit no matter how 'healthy' it would seem.
Those who drink to wash away their pain aren't burdened by grief anymore once they meet a friend who can fill the void in their soul. Those kind of friendships where each character values each other equally CAN exist in your world as well.
And if that friend falls into a slump, if that intimate partner becomes toxic, if your character feels that they can do something for someone else, then let them do it! Allow them to do what ACTUAL friends do and beat those toxic thoughts of their heads.
Not all friendships are playful and funny, some are somber and other relationships tend to never have a happy moment no matter how much those involved care for each other. However, I don't see a reason to not show and values those moments too.
Sometimes, someone can spend their entire life speaking harshly to those they care about and never get to fix their mistakes in their lifetime. They turn old and die without being able to say anything.
But life moves on. Even if a previous relationship ends in tragedy, all people have a right to seek happiness. There are those narrow-minded who say a widow should mourn her lover's death and never move on, and there are those who stay by her side no matter the wind or rain. Those who give her courage to move on towards a brighter future.
There was this slice-of-life Anime with a telepathic main girl that was hated on because it included a negative arc in the beginning (which gave readers wrong expectations) before turning wholesome later on when she meets a positive influence on her life. I myself never hated the Anime, thus I can appreciate positive change better this way.
The wrong assumption when going about characters is that just because they experienced tragedy means that they must stay sad. That they do not deserve happiness when presented to them. My advice is to let them live and move on.
No matter how melancholic, a human will never be able to stop seeking what they consider happiness and content. Some go down the wrong path, but there are also those who make the best of life.
In the end of the day, a slice of life if a genre that values human emotions even beyond their own livelihood. Just as happy moments are precious, so are those tragic moments that shaped our lives.
Characters learn to let go of certain things, but they remember to never forget the things that make them who they are. Their identity is formed from accepting every aspect of their livelihood.
Anyway, that is my take on slice-of-life. I wish you all well and stay safe in these months to come.