Hire an electrician to add an electric ceiling fan suitable for outdoor use. Position the fan in the center of the pergola. The fan can include a light.
Create a wall-like enclosure on the west wall or two opposite walls to block out sun or two create privacy. The wall-like enclosure can be created by adding additional uprights onto which lattice is attached. Or, instead of lattice, add horizontal cross beams that divide one set of uprights into thirds creating a shelf-like appearance. Divide the next set of uprights into half, the next into thirds, and continue you this process along the side wall.
Use the lattice or horizontal beams created in Step 2 to secure outdoor-safe artwork (made of metal, plastic or glass), a large mirror in the center of the wall, candle wall sconces or plant holders.
Cover the stone, brick, wood or cement floor with a patterned outdoor area rug. Outdoor rugs are designed to resist mildew and have openings in their design to allow rainwater to drain through.
Secure drapes to the top beam at each corner of the pergola extending in at least two feet on each side (just to soften the corners) or on rods that run the full length of the pergola to pull closed for privacy. The rods can be epoxy covered metal or plastic pipe and the curtains can be hung with rings. The drapes would be made of material suitable for wet areas, like that of cloth-like shower curtains.
Add faux wicker, vinyl or epoxy-covered metal furniture, which are more likely to stand up to weather than real wicker or metal. Teak or cedar furniture are also options. Choose a dining table with chairs, settee with two side chairs, or four large chairs at a large but low round table for a conversation area. Weather treated cushions and pillows can be added.
Place potted trees at the far corners of the pergola, like Japanese holly, which grows tall but has a wispy appearance.
Build a waterproof storage area along one or more walls for cushions and pillows. The storage area can be in the form of a bench for additional seating.
Run large bulb strings of clear or colored lights across the top beams and down the support beams.