Light It Up!
Some basement apartments have small windows and limited light. This can make for a dark, cramped space. Optimizing all of the natural light available to you is important so I suggest you do everything you can to encourage natural sunlight in your apartment. You can do this by avoiding any blockage near your windows or using bulbs that mimic sun rays to make up for the lack of natural sunlight available to you. Hanging a mirror on the opposite wall of a window also helps to reflect the natural light in your apartment.
Using the right decorations to enhance the space you have can lighten up any home whether it's a basement or not. Focus on enhancing the areas of your home you like most and others will notice those parts too.