Wherever possible choose a peaceful sunny room close to your bedroom. It will thus be easy to get to if the baby wakes up during the night.
Colours: Choose soft or pastel colours on the walls: bright colours are stimulating and may prevent baby from falling asleep. If you like bright colours use little touches of them: furniture, sheets or curtains, decorative objects, soft toys, etc..
On the floor prefer parquet flooring or tiles rather than carpet which is potentially allergising.
Privilege soft and indirect lighting.