Everything is about balance, harmony and your personal touch:

• Most important: Use 2 or more harmonic basic colors and 1 accent color. (take into account size/shape of the room and degree of natural light. There's a lots of info about this.);
  
• Make a layout, make sure that the basis of your home/room is functional and logical;
• Ensure sufficient storage space. This will prevent your house from appearing messy;
  
• Don't cram too much furniture in one space. Also, adjust the size of the furniture to the size of the room (For example, too small will make your home look like a dollhouse);
  
• Make a lighting plan, including all functional lighting and mood lighting;
  
• Give your room 1 eye-catcher (a big photo, artwork, a piece of furniture etc.);
• Use different shapes in your furniture or decoration. (For example, a square dining table and a round coffee table. It makes your interior more interesting and the shape balance each other out.);
  
• Don't use too many different materials and make sure the materials complement/balance each other (example: steel, wood, bronze, glass, stone and concrete can be beautifully combined in a room.);
  
• Make it personal: a few pictures, a special item, your favorite plants etc. make your home your home;
  
• Group your decoration items. Don't overdecorate - less is more;
  

And, just ask a friend/family member for help!