A bedroom need be no bigger than however much space it takes to hold the bed, night tables and any dressers, and the space to move around them.  For a queen bed, that is only about 10'x13', depending on the space required for dressers and clearance for closet doors. A bedroom is for sleeping, and using it for any other purpose often leads to conflict, unless of course you live alone.  The two other activities that are sometimes incorporated into the bedroom are a quiet sitting area, and a television, and both can lead to conflict due to lights and noise.  A sitting area can be compatible if it is only used  during daylight, or when the other person isn't sleeping.  In either case, you can get away with it if the couple's sleeping habits are highly in sync.  Especially be wary of a space in the bedroom with a computer as virtually all keyboards are very noisy.

A single bed can be in an alcove, big enough only for the bed, so that you can only get out of the bed on one side.  Kids love bunk beds, and that makes even better use of space.  A related alternative is for each child to have an upper bunk bed, and place a desk below it.  Larger beds can also be in alcoves, but if you don't want one person to have to crawl over the other, then you each need access to the opening (ie feet will face the opening).

Most people like their bedroom to have windows facing east so they can wake up to the morning light, although a bright southern exposure is nearly as effective.  Northeast facing bedrooms will have morning light, but be darker later in the day.

The bedroom should be the most isolated room in the house.  One easy way to add extra sound insulation is to located closets or bookcases on the bedroom walls to thicken up the wall between it an other rooms.

In tiny houses, lofts are the only practical sleeping space, but keep in mind that there comes a point in most people's lives when you don't want to crawl down a ladder in the middle of the night, and unfortunately you will likely have to at least once a night.