The best advice we can offer is to have design confidence. And if you don't, fake it. Search for ideas and images on design blogs (wink, wink)and in home decor magazines, as well as in your favorite store catalogs and showrooms. You will start to notice a pattern of what resonates with you and can start to determine your guiding style. However, don't get too stuck on one and only one style. It's okay to mix them up to reflect all aspects of your personality. If you have a roommate or spouse, try to find common ground and incorporate distinctive but compatible "pops" of both your preferences.
Begin with determining the function of your space. What are you going to do in this room -- eat, watch TV, play games, work, entertain friends? What purposes does the room need to serve? The function will inform the layout of the room, the pieces of furniture you'll need, and even the kind of fabrics on your upholstery. Decide what you can use from your existing furniture and then decide what you will need to fit this new space. Gradually (as budget allows) collect new pieces and stick with neutral tones for the most versatility. You can then layer color, pattern and textures with you accessories and fabrics. If you want to paint the room a color that is not-neutral, find an inspiration item (favorite artwork, fabric on a pillow, hand-painted table) and draw a color from that. Keep an eye on that inspiration item as you continue adding to the room.Jump in and enjoy the decorating process. Remember that it's really not too hard to move around artwork or furniture or even re-paint walls. What has been done can usually be re-done, so just do something to combat the fear of the white box (cue creepy dramatic background music).
How do you cope with decorating fears or anxiety? What is your best advice for attacking an empty room? What is your favorite way to fill an empty wall?