Stand in the doorway or the farthest corner and take a horizontal photo that shows the bed wall and the floor beside the bed. Make the bed and clear the floor first, since piles of clothes confuse the layout. If the room is very narrow, step back into the hallway or closet doorway to get a wider view.
Pick a calm style like Scandinavian, Japandi, or Minimalist, and describe what you want stored and lit: "keep the window and door, use a low platform storage bed, wall-mounted swing-arm lamps on both sides, floating nightstands, and a tall white wardrobe on the right wall." Clear instructions help the AI keep the furniture realistic for the room.
Generate versions with the bed in different positions, centered or pushed into a corner, and compare how much open floor each leaves. Then try one with a deeper wall color to see whether the room feels cramped or pleasantly cocooned. Keep the version you like as a reference while you measure and shop.