Do not place any lesser version of the Bed or Wardrobe in your room or you will lose stars.
i.e. if you have both a 5-star and 4-star bed, it will only count the 4-star bed.

Here's an example showing the bare minimum:

With the bare minimum done, let's see how to be a little more efficient.

The max amount of beds in each room is 5.
Here's an example of a 6 square room in a 2x3 configuration:
Notice how there's 4 double and 1 single bed. You can fit 5 double in a 7 square room, if you want.
However, that 7th square is better spent on another room.