Paint the walls of your basement. Since you are working with a blank slate, you are open to choosing any color to create the look you desire; however, you may want to consider going with a light shade to open up the space and give it the illusion of being filled with light.
Embellish the basement ceiling. If you have a drop ceiling, add interest to it with paint. Paint all of the tiles the same color or use a few colors to create an interesting pattern. If the ceiling in your unfinished basement consists of the underside of the flooring of the level above your basement and two-by-fours, decorate it with fabric. Cut several lengths of fabric. Staple one end of the fabric to a two-by-four and drape it to the next two-by-four and staple it to that, too. Continue draping and stapling the material until the ceiling is covered.
Cover the floors with area rugs. The cement floor of an unfinished basement can be cold and uninviting. Cover it with a few plush area rugs that suit the look you are trying to achieve to soften the cement and add warmth to the space.
Bring furnishings into the basement that suit the intended use of the space. To use the basement as an additional living room, a couch, armchairs, a coffee-table, side tables and an entertainment center filled with audio-visual equipment are ideal additions. If the space will be used as an office, bookshelves, a desk and a comfortable desk chair may better suit your needs. For a multifunctional space, bring in all of these furnishings.
Add decorative accents to complete the look of the basement. Frame pictures and set them on any pieces of furniture you have brought into the area. If you wish to hang pictures on the walls, use adhesive tape and hooks to do so. Fill vases with flowers and set them on tables. Place large potted plants on the floor. Fill baskets with blankets and pillows to use to keep warm if the space gets chilly.