Guest bedrooms, no matter what style, need to have character and neutrality all at the same time. Your guests want a space that is memorable that they will want to return to, so I always steer clear of going overboard with color.
It obviously depends on the client, but I prefer to use blackout window treatments that are sometimes a design detail, like drapery, or sometimes hidden away and tucked into the architecture of the room. However, I never forget to have a spare eye mask in the bedside drawer.
I also layer a variety of bed covers. Everyone sleeps differently, so I make sure there is something lightweight and something heavy. I also tend towards bedding that is easy to keep neat and not too complicated. A guest should have the option to throw the bed back together in the morning.