If your ceiling tiles are looking a little dingy but the ceiling grid is still in good shape, paint your tiles to add color to your ceiling. A basic coat of primer followed by a coat of paint will cover most light to medium tile stains. Use a foam roller to paint each tile to keep from applying too much pressure to the tile as you work. Old ceiling tiles are often fragile and prone to breakage. If your ceiling grid is visible, be sure to apply a coat of paint to the grid to freshen it up.
For a quick fix in an apartment or other space, bunch up material using strings and hooks across the ceiling to cover old tiles, or cover each tile individually with fabric. Use a simple starch and water mixture to coat the back of the fabric, and apply it to each tile. You can cover all tiles with the same fabric in a single bold color or simple pattern, or you can mix it up to create a patchwork quilt effect.
If fabric isn't for you, add wallpaper to your ceiling tile squares, You can cover each ceiling tile individually, or if the tiles create a relatively smooth, flat surface, apply the wallpaper across the whole ceiling. Fill in any place where the ceiling tiles meet with a filler or caulk to create an even smoother surface to apply the wallpaper. Choose a simple colored cloth wallpaper or a more intricately patterned wallpaper to create a more unusual look.