Dont add smells... your viewers may have different tastes to you. I remember shopping for my first house, and being put off by the fug of scented candles EVERYWHERE, which I just can't abide. Instead concentrate on clean and really well aired, which nobody can object to.
Light each room the way you'd want to use it... For living rooms/bedrooms/dining rooms, that's probably cosy, low-level lighting, curtains drawn, fires lit (if you can count on them staying lit and being safe) or laid for lighting (if they might engulf the room in smoke left unattended!) obviously, for viewings in daylight, lights off, curtains and blinds right open, not at half mast! If you leave the lights off, they'll just switch on the central lights, which isn't always the best look.
Make it tidy, but not clinically so. Use your judgement about the scene you want to set. A novel left open on a coffee table in an otherwise tidy room suggests a relaxing evening. A laptop, mobile phone and a sheaf of papers on the coffee table suggests no proper workspace. Salt and pepper mills on the dining table suggest a useable dining area. Last nights dinner things on the dining table suggests a hangover.
Absolutely agree that mirrors and windows (plus any glass light fittings) should be sparkly clean. Same really for anything that should be shiny or white (tiles, sinks, skirting boards, light switches, window sills, French polished furniture, dishwasher fronts...) Repeat often, because they don't stay like that for long!
Get an honest/rude friend in to give it the once over before you throw yourself to the real wolves!