Shoot from the doorway or the corner farthest from the window, holding the phone level at about chest height. Clear bags and laundry off the floor first, since the AI treats every object in the frame as part of the room. A wider view showing two walls and the floor gives much better layout results than a close-up of the sofa.
Pick a light style such as Scandinavian or Minimalist and describe the scale you need: "keep the walls, window, and radiator, use an apartment-size light gray sofa on legs, add a round coffee table, shelves to the ceiling on the left wall, and a mirror beside the window." Size words like apartment-size or slim help keep the furniture proportional to the room.
Run a few versions with different layouts: sofa under the window, sofa facing the window, or an L-shaped arrangement with one chair. Compare which leaves the clearest walkway and which feels most open. Treat the image as a visual check, then confirm real dimensions with a tape measure before you order anything.