When decorating your home there is no right or wrong. That said, Designers use guidelines when planning space. Following are a few essential rules of thumb.
When selecting the size of a chandelier take the width of the room in feet and double it. convert that to inches and that is the minimum size chandelier you should consider.
30-32” is the approximate height to hang a chandelier over a dining table.
When purchasing a new sofa consider the ergonomics of “the sit”. What is comfortable for most people is a combined measurement of the seat height and depth of 40-42”.
If you are in love with something out of your budget use it in a small area that will give you a big look. For example use an expensive wallpaper in a powder room or make pillows out of a pricey fabric.
When deciding on the size of an area rug bigger is generally better.