Don't Design Every Room Separately
Sometimes people want to use their room as a place to constantly experiment and shift their design perspectives. That's a perfectly reasonable thing to do. However, houses can seem chaotic if every room is a different work in progress...
Focus on the Big Picture
Every room in a house should be styled at least similar enough to seem like they belong in the same space. If one of your rooms is pink and covered in flowers, and the rest of your house is painted matte black with white accents on the walls, that's going to clash.