[@BrokenPromise] and [@Ammokkx] basically covered the gist of it, but one thing that can help is spending time reading the posts of writers you like and paying attention to the details they put in; do things like engage the senses, think of body language or how a character would physically do an action; are they hurt or tired? What's their emotional state? Try to put yourself in the scene and imagine what it all looks like and feels like, what other small details exist that can help establish the scene. What kind of ambient sounds are in the area? Are there birds or other animals? Can you hear cars or water? There is so much you can do!

Alternatively, maybe try reading a novel or two and see how the author fills out a chapter. I would also strongly recommend collaborating with people in your roleplay! Open a gdoc and write a post together.