Make a Plan
Just because the room is going to serve a double purpose doesn't mean the physical space has to be evenly split, with half the area serving as a dedicated office and half as a guest room. Instead, the space you allocate to one function should be proportional to how often it's used. For example, if you work in your office almost every day but only have overnight guests a few times a year, most of the room should be a work area, with the remainder serving as a guest refuge. Remember, this is all about smart design and functional living.