Continuity mistake: In the beginning of the movie when the guardians are getting ready to fight off an interdimensional being Rocket winks a couple of times at Starlord. Starlord then responds but is looking to his left at Rocket, whilst Rocket is on his right side. The scene is for no reason mirrored, proven by the big orange device behind him also switching from being on his left to on his right. (00:03:45)
Revealing mistake: When Taserface is threatening Rocket, Rocket is making eye contact. Taserface, meanwhile, is looking at the space between Rocket's ears.
Continuity mistake: When Pete is holding his hands out, as per Ego's instructions, the orientation of his hands changes. Initially, his thumbs are roughly at the top, but when the camera angle changes, they are at the side. No time has passed, and Ego didn't tell him to change anything.
Continuity mistake: While Yondu is explaining how he tracked the Milano, and who sent him and why, look at the 3 arrows pinned to Yondu's jacket when he first appears. Once he starts his walk around while explaining, there are only 2 arrows. After the scene returns from Nebula and baby Groot, the shot seems to be mirrored, with the three arrows in a different position. (00:40:15)