One great RWBY Guardians of the Galaxy fanfiction is 'The Cross - Over Adventure'. It combines the unique worlds of RWBY and Guardians of the Galaxy in a really fun way. The characters from both universes interact in a believable manner, and the action scenes are exciting. It has some really cool plot twists that keep you hooked from start to finish.
In some fanfictions, the threat that unites them helps in blending the worlds. Say there's a powerful enemy that can only be defeated by combining the powers of both groups. This forces the RWBY characters and the Guardians to work together. The RWBY characters' Semblances and the Guardians' unique abilities become complementary. And the different settings, like the planets in Guardians of the Galaxy and the kingdoms in RWBY, create an interesting backdrop for the story.
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.
Well, Tumblr can be a great place too. There are often users who share their Guardians of the Galaxy fanfiction pieces, either directly on their blogs or by reblogging others'. Additionally, Wattpad might have some interesting takes on Guardians of the Galaxy stories, although it has a wide range of content so you may need to do some searching.