First, you need to really understand the characters of Rick and Morty. Know their personalities, their quirks, and how they interact with each other. For example, Rick is cynical and brilliant, while Morty is often naive but has a good heart.
Create an interesting setting. Since it's a lemon - themed fanfic, you could have a setting like a lemon - scented alien planet or a dimension where everything is made of lemonade. Make sure the setting impacts the story and the characters' actions. Also, think about the plot. It could be a mystery, an adventure, or a comedy. For instance, Rick and Morty could be on a quest to find the rarest lemon in the universe, which has some amazing power. And don't forget to write good dialogue that sounds like the characters from the show. This will make your fanfic more engaging and true to the Rick and Morty spirit.
When writing a Rick and Morty lemon fanfic, it's important to be creative. You can play with the concepts of the show in new and unexpected ways. Maybe introduce new characters that are related to the lemon theme, like a lemon - headed alien who becomes their friend or foe. Also, pay attention to the pacing of the story. Don't rush through the plot, but also don't let it drag. Keep the readers interested by having a good balance of action, dialogue, and description. And always proofread your work to make sure there are no grammar or spelling mistakes, as these can take away from the overall enjoyment of the fanfic.