So, what I found to be a great way to help with the pacing of the story is to add sub plots. So, normally with my subplots they give you an insight into non-main characters’ backstories to give them more texture and personality along with helping the reader understand main characters through interactions they may have with the characters.
The thing with subplots are you can pull them off if you intertwine them with the main part of the story/main premise of the story - personally, I am a sucker for sub plots because it helps pace the story out. My story is more of a slow burn romance so the pacing will be a bit slow anyway so to help add more information/entertainment I add subplots to make things a bit more interesting.
I recommend making a diagram/flow chart and have a rough idea of a beginning, middle and end. Is there a conflict? How will the protagonist overcome issues? In the end, will the aim be achieved or will it be open ended?