If you are staying nearby in Wiltshire, consider getting a two day ticket. This is considerably cheaper than two individual tickets and provides the possibility of splitting the house and gardens between separate visits.
Longleat is most famous for its safari park. Arrive early and head to the safari gates right away as it gets very busy by afternoon. It takes around two hours to go through the entire safari experience. Also outside the house is the famous maze, formal gardens, parkland, playgrounds and a river boat cruise.
Longleat is home to the Marquess of Bath and his family and visitors can explore the public rooms. Make your way round the ground and first floor at your own pace, making sure not to miss the spectacular Great Hall with its world class art collection.