When designing a modern space, the first step is to get rid of (or at least hide) any unneeded clutter. Once the room is cleared, add a few multifunctional pieces. Be sure that every element you bring in has a clearly defined purpose in addition to driving home your modern aesthetic. Carefully distribute items throughout the room so that it feels balanced.
Modern interior design came about as a reaction to the ornate and almost baroque styles that came before it. As such, the main focus of this school of design is to act as the antithesis of of those other looks. Rather than having lots of details and embellishments, modern furniture relies on clean lines and stark contrasts.