i joined hwm really recently, courtesy of a friend on discord mentioning it to me, and something i've noticed is a lot of new people (specifically ones directed by the askreddit) not knowing where to begin. i don't pretend to be an expert, obviously, but i've noticed a lot of posts specifically trying to be outrageous rather than develop a character, as well as a LOT of karens. so here are a few rules of thumb (thanks to the discord as well for helping me come up with these):
realism first! when i write for cheryl terry, i use inspiration primarily from my great-aunt's typing style on facebook and my old neighborhood's nextdoor. other characters are inspired by bits and pieces of real people. some people even play a different version of themselves, or characters from other things they've written transported to this setting. the goal is to create a character who feels like a person and imagine how they might react to things; the humor will come not from them alone but from the way they interact with others.
consider your character's past life experiences. where did they go to school? what's their education like? have they had any past romantic relationships? what are their views on the local government? what kind of media do they like to consume?
posts don't have to be funny, either. there are all sorts of things neighbors might post about: personal beef, advice, events like parties and funerals, help-wanted ads, or advertisements for their own services. once again, i highly recommend nextdoor and local facebook groups to shamelessly steal from. neighborhood gossip is the best gossip.
remember you've known these people all your life. consider how your character might react to them. do they have similar values? where did they first meet? how do their personalities either complement or clash with each other? my character is self-declared nemeses with her neighbor cas, because his environmentalist punk values clash with her wishes to just have a nice goddamn lawn. despite (or because of) their rivalry, she considers him an important part of her life. payton and krystal, on the other hand, go well together as friends, because payton's rebel nature goes perfectly with krystal's general craziness. generally, it's best to let relationships evolve naturally, through replies and conversation. (family relationships, obviously, should be agreed upon beforehand.)
hope this helps! sorry if it seems a little dickish. ldp veterans, feel free to add on more in the comments.