Begin by immersing yourself in the world of 'Pitch Perfect'. Watch the movies again to pick up on all the little details about Bechloe. When you start writing, let your creativity flow. You can take inspiration from other fanfics but make it your own. Maybe set your story in a different time period, like in the 1980s where they have to adapt their acapella style to fit the era. Develop their characters further by giving them new hobbies or fears. And most importantly, write with passion and love for the Bechloe pairing.
First, really study the characters of Bechloe from 'Pitch Perfect'. Get to know their personalities, quirks, and how they interact in the movie. Then, come up with an interesting plot. It could be something like them going on a road trip together or facing a new musical challenge.
To write a 'bechloe pitch perfect fanfic', start by creating a strong outline. Decide on the main conflict or goal for Bechloe. For example, maybe they're trying to save the acapella group from disbanding. Next, focus on their relationship development. Add in some cute, flirty moments between them, and don't forget to include some of their trademark banter. Also, make sure to use vivid descriptions of the settings, like the rehearsal rooms or the concert stages.