If a room is used for a number of purposes then it makes sense to define the area used by each with either a physical divider or by change in decoration. This is particularly the case in loft apartments where one large space may be used for cooking, eating, lounging, working and sleeping but it is also important in a kitchen 
diner, a studio bedroom or a combined living room study or dining room.
Rooms can be divided by:
Full or Partial Walls
Partition walls are easy to install and these can be full height or they can stop short of the ceiling allowing light to flow through. They can be made of solid material or glass, the latter allowing more light to pass into the partitioned section of the room.
Furniture
Shelves and bookcases which can be accessed from both sides are excellent as room dividers and as they are open they do not block the light. Screens are also useful especially those in keeping with the overall decoration of each area.
Doors
Sliding or folding doors can allow the room to be opened up when required and then divided at other times. They are very useful if you want to use the room in different ways and don’t always require it to be sectioned off.
Fabric Panels
Blinds or Curtains can be hung from the ceiling to help partition a room. They do not block sound but they are unusual and are a wonderful decorative way of adding a room divider.
Flooring
A change in flooring is a good way to divide up a room. You may decide to have carpet in a seating area of your lounge and then change to oak wood flooring for the dining area. This change can be emphasized if there is a change in floor level too with some activities on a slightly raised platform. Floor rugs can also be used to create separate areas. For example, in a kitchen diner the kitchen part may have no rug whereas the dining area may be situated on a large area rug.
A Change in Colors
You can use different (coordinating) colors to pick out the various areas of your room. For example a white kitchen might have a dining area with a brighter focus wall or a living area with neutral walls, a purple rug and cushions on cream sofas may have a dining area with neutral carpet and a purple wall.