No need to do much for enlarging a room or create perspective. You just have to know how to use paint to transform your interior. Here are some ideas for using optical effects properly:
Light Colored Walls & FloorsLight colored walls and floor would have an enlarging effect and would also enlighten the room. You'd better chose one color only from floor to ceiling: it won't draw attention to the corners, the room will then seem larger. Light teints (wood, white, light brawn) would also perfectly match with colorful furniture. 

Dark floor, light wallsA dark floor would make an enlarging effect and give more character to your interior. That is the reason why it is mainly advised to have a floor slightly darker than walls. Grey or black floors can be very elegant but they would also draw attention on the floor only, overlooking the rest of the room. What's more, pay attention to colorful floor, your eyes might get tired of it very quickly! 

Light floor and dark wallsDark walls - with light floor and ceiling - would seem higher and deeper but also very tight. You should also have a very bright room if you want to use a dark painting, so that your interior doesn't seem too dark - pretty much like a shady basement. 

Light floor and walls, dark ceilingA dark ceiling would make the room lower. Nevertheless, if you have a high ceiling, painting it might be a good idea, it will give the space some colorful energy and transmit light from the different ceiling lights. 
Colorful nichePainting a niche will allow gaze to escape the room and create the illusion of an open space. Use of a colorful canvas or mirror would have basically the same effect. 

Paint one wall onlyPaint one or two walls instead of all of them modify the organization of space and contribute to make it larger and more open. Paint the wall at the back with a strong color will enlarge the room. For example use it at the end of a tight corridor. Be careful if you decide to paint lateral walls, it will make the room longer but tighter.

 Play with linesHorizontal lines will open the room in its width. Vertical lines will extend the space to the back of the room. Then, it is strongly advised to use line perpendicularly to the longest walls in order to enlarge the room. 

Vertical lines on the walls (or curtains) will stretch the wall to the ceiling, whereas horizontal lines will make the walls wider.
  

Pay attention not to select too big lines in small interiors. It will make the room smaller. 

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