When you consider redecorating, take time to study each room carefully. What is the purpose or fuction of the room? A place to relax? A playroom? A mancave? A place to gather with friends?
Then, consider the features of the room. Does it have a fireplace, or a bay window, or perhaps built-in shelves?
Redecorating could be as simple as re-arranging furniture, adding accent pillows or slipcovers for tired furniture. Consider wall color. If it is meant to be a calm space, stay away from reds and yellows - go for greens and blues.