It is important to leave the floor free to make a small pooja room look bigger. A clutter-free mandir with warm lighting will also look substantially bigger. In addition, it will be beneficial to create a space for worship in the apartment using a wall-mounted unit, a niche or a cabinet with a back panel.
Finally, it is important to choose wisely the location and the furniture for a small pooja room. A minimalist design with warm colors and lots of natural lighting will make such a room comfortable and welcoming.