Take a photo from a corner of the room at chest height, in landscape orientation, with overhead lights off and daylight coming in. Include as much floor as possible and at least one window so the AI can read the room's scale and light. Avoid heavy distortion at the edges: stepping back and using the standard lens gives cleaner results than the ultra-wide camera.
Choose the Modern style, then add a short instruction that names what to keep and what to change. For example: "keep the windows, flooring, and fireplace, replace the sofa with a low charcoal sofa on a wool rug, add a travertine coffee table and an arc floor lamp." Specific nouns and materials work better than vague adjectives like nice or clean.
Generate two or three variations, changing one thing at a time: the sofa color, then the rug, then the lighting. Put the results side by side and decide which elements you would actually buy. Save the version you like most and use it as a shopping reference, so your purchases follow one plan instead of a series of separate guesses.