Think about the style and the theme that you want to set for the mehendi party. Since it is a private affair, wherein only the close female relatives (apart from the family members) are called upon, keep the theme simple.
Decorating the place with fresh flowers and scented tea-lights is a nice idea. It will set a lovely ambience for the ceremony. Wind chimes, hung at the dividers of the rooms, would add to the overall appeal.
Hang a string of bells at the entranceway of the place. You may also welcome your guests by hanging a small banner at the entranceway.
Ensure that you provide the home with enough lighting. It is wise not to resort to dim lighting, because it is mehendi ceremony, wherein intricate designs of henna are carefully applied on the bride's hands and feet. Hang a crystal chandelier at the place, where the mehendi is applied.
The mehendi party mood can be reflected by making use of henna color scheme for the entire place. Arrange henna-colored throw pillows on the couch. Use shades of green for the comforters, bedding, table cloth and curtains. Choose the right shades of green for the purpose. Bring in variations by making use of contrasting shades of the color.