Focus on practical décor that complements your wall colours. Wooden furniture instantly adds cosiness to a room. Use curtains in neutral colours like white to create a clean and balanced look. Cushions in darker shades like crimson red can add texture and make the room more comfortable.
Basically, to make a room feel cosy, you need to add more natural elements and remove harsh ones like stark white lights. The exact nature of these elements' changes based on the room and what it is used for, but the ways to go about it are pretty easy to understand and implement.