Something I feel I should add here (I will also put this on the opening post)...
When embarking on writing (be it fanfiction, original, etc.), I cannot stress enough that you take your time! Pace yourself.
DO NOT RUSH. Especially if you realize that you
have hurried your composition and you yourself notice the adverse effects it has on your work, you need to slow down and give it the attention it requires and deserves.
Rushing a chapter, hurrying to get something done and posted, is often a detriment. You end up with not only missing grammatical and spelling errors, but also the richness of the content suffers. For example, you devote much less time to meaningful dialogue and character relationships as a result. You also may not address important plot points or present plot devices in as meaningful of a way as you might have desired or planned to, and the narrative can certainly suffer for it.
So my advice is this: I understand that having content to post frequently is something that keeps people aware and interested in your work. But you are doing yourself and your story a disservice if you know you are moving too quickly and you find yourself having to apologize for things seeming "rushed". My "Kathodos" chapters, admittedly rather long these days, take me anywhere from 3-5 weeks on average to write. That's partly because I work full time and it's a free time issue. But it's also because I want to make sure that I'm addressing what I need to address, including what I mean and need to include, and keeping an eye on technical mistakes.
Some people naturally write more quickly than others and that's fine. But just make sure that you're doing right by your story and giving it the time and attention it needs and deserves. It will more than likely pay off.