The plot is crucial. You could start with an interesting premise like your OC being on a mission that crosses paths with Asajj Ventress. Build tension and conflict in their relationship, whether it's a rivalry or an unexpected alliance. Make sure the story flows logically and has a clear beginning, middle, and end. Also, use vivid descriptions to bring the 'Star Wars' universe to life. For example, describe the different planets they visit, the battles they engage in, and the unique cultures they encounter.
You can try fanfic websites like Archive of Our Own (AO3). It has a large collection of 'Star Wars: Clone Wars' fanfics. Just use the search function and type in relevant keywords like 'OC x Asajj Ventress'.
I really like 'Ventress in Love'. It's a unique take on her character as it gives her a romantic storyline while still maintaining her badassery. It's not your typical Star Wars story but it works really well with her character. There's also 'Ventress: The New Alliance' where she teams up with some unexpected characters and the story unfolds in a very exciting way.
One possible fem clone OC could be a highly skilled sniper. In fanfiction, she might have unique markings on her armor that distinguish her from the male clones. She could befriend some of the Jedi, like Ahsoka Tano, and together they face various challenges during the Clone Wars.
One interesting clone fanfiction could be about a clone's journey of self - discovery outside of his military duties. For example, a clone might start to question the purpose of the war and his place in the galaxy.
One unique plotline could be a time - travel story. A character goes back in time to the start of the Clone Wars and tries to prevent certain events from happening. Another could be a story where the clones develop their own culture and start to question their purpose. And there's also the plotline where a Jedi falls in love with a Separatist, creating a conflict of loyalty.
You can start by looking on fanfiction websites such as Archive of Our Own (AO3). It has a large collection of fan - created works, including many for 'Star Wars: The Clone Wars' and specifically about the clones.
Themes in this type of fanfiction can be quite diverse. The idea of self - discovery is a big one. Clone troopers start to question their purpose and place in the universe. Another common theme is the relationship with the non - clone characters, be it the Jedi, the civilians, or the Separatist forces. How they interact and how their relationships develop is often explored. And of course, the theme of following orders versus doing what is morally right, as clone troopers are trained to follow orders but sometimes face moral dilemmas during the war.
By showing different perspectives. For instance, in regular 'Star Wars Clone Wars' we mainly follow the main characters. But in fanfiction, we can see how minor characters react. This gives a more complete view of the universe.