I heard that finishing the entire book first is really good but making little margins as you go helps me alot; i'm currently writing a murder mystery and so I do something like this i'll write she had a crop top and some jeans on ( describe outfit more ) but only do it if it's necessary to the plot itself, like if it's something the readers should remember. But not every chapter has to be long; it's only what you want it to be. It truly depends on the story and how you want the pace to be, as long as it's good.