First, understand their characters well. Twilight is intelligent and studious, while Spike is loyal and eager to learn. Start with a simple scenario like them sharing a book in the library. Build on their conversations, showing how they care for each other's opinions. For example, Twilight could be explaining a complex spell to Spike, and Spike could be asking interesting questions. Then, add some conflict, like a new pony in town who misunderstands their relationship. Finally, resolve the conflict in a way that shows their love for each other, whether it's friendship - love or a more unique bond.
When writing a 'Twilight Sparkle and Spike love fanfiction', think about their personalities. Twilight is often focused on her studies and magic, so you could have her use her magic to do something special for Spike, like create a custom book for him. Spike, on the other hand, can show his love by helping Twilight with her daily tasks. For the plot, you might consider a mystery where they have to work together. As they solve the mystery, their relationship deepens. Also, don't forget to include their unique interactions, like Spike's cute little dragon habits and Twilight's sometimes - nerdy magic talk.
To write this type of fanfiction, start with a strong concept. Maybe it's a story about how Twilight and Spike first met and how their initial connection grew into love (in a non - romantic or platonic sense). Develop their relationship gradually. You could include moments where Spike defends Twilight from mean ponies or Twilight teaches Spike an important life lesson. Use descriptive language to bring out their emotions. For instance, when Spike is happy, describe his little dragon tail wagging. And when Twilight is proud of Spike, show it in her eyes and the way she smiles at him.