Make sure your windows aren’t obscured by heavy drapes, net curtains or Venetian blinds.
If privacy isn’t an issue allow the maximum amount of light in to bring light and life into the room.
Clever use of mirrors can amplify the effect. Sight lines are important though. Make sure to take account of what people are going to see reflected in them.
Try to position the mirrors to highlight the best features of the room.
If you are using a particularly large mirror use one with sectioned panels so that the room doesn’t end up looking like a shop.