Keep the colors light:
Colors like white, neutral and soft shades make an apartment feel and look bigger. Use them on the walls. Try to use monochromatic colors and subtle contrasts instead of sharp contrasts which tend to give a separated look to a space. Light colored walls reflect light and give an airy feeling while dark ones absorb it making a room look smaller.
Use both natural and artificial lighting to brighten up your apartment. Dim lighting gives off a feeling of dullness and makes the space feel smaller by creating shadows. Avoid heavy curtains. Keep the windows open during the day to let natural light in.
Mirrors are smart objects. They have functionality, can be used in decoration and to create an illusion. Use the last purpose to your benefit. Cleverly place mirrors around the apartment in a way that they give an illusion of greater space. Mirrors also reflect light and bounce it across the room to make it feel more spacious.
Reduce the clutter:
Even large apartments feel cramped up if there is too much stuff and worse if the stuff is not organized. Keep everything in place and designate spaces for them. Avoid piling up laundry and waste. Give away anything you do not need. Keep only the best of decorations and paintings. Try to have a clear floor plan so that you do not keep bumping into things.
Be smart with furniture:
Get furniture that has multiple functions, like a sofa cum bed or a sofa with a book rack under it. Keep the furniture colors light and cut on the dark wood. Try to match the colors of the furniture to the wall color. Place large furniture pieces against the wall to maintain a space in the middle. Arrange furniture in a way that it does not block pathways. Prefer buying furniture in large pieces instead of several small ones like a three seat sofa set instead of three individual sofas. Look for furniture that is slim and not very stuffed up.