If you are fortunate to have a large bathroom, it does not mean that any less planning is needed. You still need to take into account the position of plumbing fixtures, whilst maintaining enough space around each of your fittings. Simple things must be kept in mind such as having a space to store towels near your bath so that you do not have to walk across the bathroom when you get out of the tub. Grouping fixtures together will allow you to use the extra space created for additional relaxation areas, or for space to install fitted cabinets and other storage areas.
You may wish to think about providing a focal point for your bathroom; this can be centred on the bath to create a feeling of luxury within the room. A large room will accommodate a much more extravagant bath. Such a bath may be a freestanding model, or a large hydrotherapy or whirlpool bath, allowing for extra comfort within the bathroom. If the room is to be shared, then perhaps you might consider using dual basins to allow more than one person to use the room at the same time. While lighting will not be as important to create a feeling of space, it must still be considered carefully. If you wish to create a degree of intimacy within your bathroom, then you may wish to choose darker tones and colours to make the room seem cosier. You should also make sure that light can reach all areas of the room effectively by planning your lighting around the natural light provided by any windows, and making sure that the areas not reached by natural light are properly illuminated. Variable lighting could be used in order to highlight the more prominent areas, or mood lighting could be used to create a very personal feel to the room.
When thinking about furniture, you do not have to be bound by the constraints of fitted cabinets, and can instead experiment with more unusual ideas for storage. You could make use of freestanding cupboards for towels, or have a larger cabinet in which to keep any toiletries. You could even make use of a moveable storage unit, which provides convenience without clutter. Having extra space means there is more scope for extending the use of the bathroom. You have the opportunity to install a dressing table and mirror, or additional relaxation/exercise equipment to truly individualise the space.