Almost everyone working in mainstream comics started off as a starry-eyed kid reading and loving comics. We're all fans, and that's great. But when we start working on company-owned comics professionally, we have to think like storytellers instead of fans. Editors aren't looking to hire the biggest fans of the characters. They're looking to hire the best creators with the best ideas.
Don't slag off other creators or companies. We'll cheerfully mock dumb politicians on Twitter, but we try to never slam another creator's work or make fun of another company's projects or initiatives. First, because life's too short. We'd rather use that time to celebrate the fantastic work of colleagues and friends. Second, because it's a small world, and people have long memories. A few snarky words today can ruin a chance for an incredibly rewarding creative partnership tomorrow.