Writing a great Naruto fanfiction with an OC also involves creating a unique plot. Instead of just following the same storylines as the original series, come up with something new. Maybe your OC discovers a hidden ancient power that the main characters don't know about. This could lead to a whole new adventure. Also, use vivid descriptions to bring the Naruto world to life. Describe the scenery, the battles, and the emotions of the characters. And make sure your writing style is engaging. Use dialogue effectively to show the personalities of your OC and the other characters. If you can do all these things, your Naruto fanfiction with an OC has a good chance of being great.
To write a good Naruto fanfiction with an OC, you must study the Naruto universe thoroughly. Know the rules of chakra, the different ninja clans, and the political landscape. Your OC should abide by these rules. For instance, if your OC wants to learn a new jutsu, they should have a legitimate way to do so within the Naruto world's framework. Additionally, develop your OC's relationships. They could befriend some characters and be rivals with others. These relationships will drive the plot forward. And don't forget about character growth. Your OC should change and develop as the story progresses, just like the canon characters do.