Other spaces can be utilised - a lobby, a corridor or hallway, a corner of the lounge or dining room, the attic, basement, or garage.
A traditional office desk won’t make you any more productive, so consider double-dipping if necessary. Many successful businesses started life on the dining table. Consider a standing desk that can easily be achieved with two beer crates and an old door.
If none of these spaces are available, then set an office up in your bedroom and separate it from the rest of the room with a wardrobe, bookshelves, a curtain or a screen.
To make the best use of space, build up rather than out. Narrow bookshelves extending from floor to ceiling take up less room, and offer more storage space, than chunky chests of drawers.