Actually, the best interior for a guest bedroom is one that is comfortable, inviting, and makes your guests feel at home. You can never know which interior style is guest's favoutite, so it is better to choose something neutral for every design item. First of all, remember about the neutral color scheme, such as beige, white, or grey, can create a calming atmosphere that's perfect for guests to relax and unwind. Of course, think about the space, I guess your guests would definetely appreciate having a place to store their belongings. Make sure there's enough space in the closet or dresser for them to unpack and settle in. But still, I think that it is also important not to ruin your overall home interior style, so to look at the succesfull examples of designing a guest bedroom I recommend to look through spotless agency   https://www.spotlessagency.com/portfolio/second-bedroom    portfolio. That will give you great ideas and suggestions how to match the guest bedroom to your actual home design.