Another factor is the exploration of themes. It could be about love, friendship, or redemption. If it's a love story, it should show how the OC and Gamora gradually fall for each other in a believable way. It should also stay true to the overall tone and lore of the Guardians of the Galaxy. For instance, respecting the different species and cultures within the universe. Plus, a touch of humor, like the kind we see in the actual Guardians of the Galaxy movies, can make the fanfiction even more enjoyable.
You can start by looking on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. AO3 has a large and diverse collection of fanfics, and you can use the search function to specifically look for 'Guardians of the Galaxy OC x Gamora' fanfiction. FanFiction.net also has a lot of works in this category. Another option is to check out some Guardians of the Galaxy - related forums or communities where fans might share and recommend their favorite fanfictions about this pairing.
The Guardians of the Galaxy comics are known for their humor. The combination of the characters' personalities and the creative storylines contribute to the funny aspect. Some issues are funnier than others, but overall, they have a good dose of comedy.