By taking a few precautions, you can reduce dust in your unused guestroom even though the room doesn't see a lot of activity. If the room is relatively dust-free, you'll have less cleaning to do on the rare occasion in which the room will house some guests.
1 - Cover Furnishings
Beds, chairs, desks, shelving and other furnishings that don't see much use in your guestroom are dust magnets. It's simple to reduce dust by covering all of these furnishings with tarps or cloths when not in use.
2 - Don't Leave Linens Out
Bedding, clothes, towels and other cloth items attract dust when not in use and can be especially difficult to clean without washing. Make sure that none of these items are out in the room when it's not in use. That means the bed should be unmade until you have guests over.
3 - Use Dust-Reducing Products
When you do dust, don't simply shift the dust around with a feather duster. Use a static duster that picks up and traps dust and spray all solid surfaces with a dust-reducing cleaning product. These products keep on working to repel and reduce dust between cleanings.
4 - Run an Air Cleaner
Every so often, you should let an electronic air cleaner run in your unused guestroom. These air filters can help circulate air and trap dust particles, thereby helping to reduce dust in the room.