Add lots of details about their emotions. For example, describe how Eleven's heart races when Mike leans in for the kiss. This makes the readers feel more connected to the characters.
Their relationship could also face challenges. Maybe the other members of the group start to feel left out, which causes some tension. But Eleven and Mike work through it together, showing that their relationship is strong enough to handle external pressures. They could become more protective of each other, too, especially when it comes to facing the supernatural threats in Hawkins.
Fanfiction writers usually paint the first kiss between Mike and Eleven as a very emotional and significant moment. They may describe the light, like how the sun is setting or the moon is shining, creating a romantic backdrop. There could be a focus on their breathing, becoming more rapid as they get closer. And the actual kiss is often described as a moment of pure connection, where the world around them seems to fade away.
No, it is not appropriate. 'Stranger Things' is a popular show mainly targeted at a wide range of audiences including younger viewers. Writing fanfiction with sexual content about the characters goes against the family - friendly nature of the show and can also be considered disrespectful to the original creators and the young fan base.
The 'Mike and Eleven First Kiss Fanfiction' that I thought was great was one where they were in the woods. They had just escaped from some bad guys. In that moment of safety, they shared their first kiss. It was like a celebration of their survival and also the start of a new chapter in their relationship. The description of the forest around them added to the overall atmosphere of the story.
One idea could be that they share a kiss during a moment of great danger. Maybe they are facing a powerful enemy and think it might be their last chance to express their love. So, in the heat of the moment, they kiss passionately, giving them the strength to fight back.
One idea could be that Eleven and Mike's kiss is a moment of reunion after being separated for a long time. Maybe Eleven was lost in the Upside Down again, and when she returns, the kiss is a powerful expression of their love and relief at being together once more.
You could also check out some fanfiction review blogs. These blogs are dedicated to reviewing and rating fanfictions. They might have a section for Stranger Things and within that, you can find reviews of Mike and Eleven fanfiction, which can help you decide which ones are worth reading.
Create a mystery element. Maybe there are strange disappearances in the underwater kingdom that Ariel has to solve. It could be related to an ancient curse or a new threat that no one has seen before. This would keep the readers on their toes.
Add a lot of mystery. Don't reveal all the details of the deal right away. Let the readers wonder what exactly the devil is getting out of it and what the full implications of the deal are for the character. For example, if the deal is about getting revenge on someone, make the revenge seem simple at first but then show how it spirals out of control.
There's a fanfiction called 'Eleven's New World with Mike' which is really interesting. In this, Eleven discovers new powers and Mike is right there with her every step of the way. It delves deep into their emotional connection and how it evolves as Eleven changes.