When you buy furniture for your apartment, buy wisely.

Your furniture must be compact. Otherwise it will overpower the space and make the apartment seem small and poky.
Before you go shopping, use a tape measure to take exact measurements of the dimensions of your apartment. Draw a floor plan to scale, and take it with you to the furniture store. Measure each item of furniture, and make sure there is at least 45cms of clearance (18 inches) anywhere you are planning to use as a through-way.

Look for furniture that doubles as additional storage. Beds and coffee tables with deep drawers underneath. Box-seats. Bedside tables with drawers. Side tables with drawers or shelves. Desks with returns above the desk surface, and file drawers below.  

Tip: to add character to your apartment (which will probably be a boring box shape) buy furniture basics at the retail outlet of your choice, and then go to antique shops or auction websites like ebay to pick up a feature item or two for each room. Choose something with curves, luscious fabric and/or a distinctive colour. If you tend to be particularly bold in your choices, buy the feature items first and then build the rest of your decorating scheme around them.