COMPARISON OF ADJECTIVES
COMPARATIVE + THAN

To compare the difference between two people, things or events.

Examples:

  • Mt. Everest is higher than Mt. Blanc.
  • Thailand is sunnier than Norway.
  • A car is more expensive than a bicycle.

  • Albert is more intelligent than Arthur.


THE + SUPERLATIVE

'the' is placed before the superlative: 

For example: He is the richest man in the world.
 

AS + ADJECTIVE + AS

To compare people, places, events or things, when there is no difference, use as + adjective + as:

  • Peter is 24 years old. John is 24 years old. Peter is as old as John. 
More examples:
  • Moscow is as cold as St. Petersburg in the winter.
  • Ramona is as happy as Raphael.
  • Einstein is as famous as Darwin.

  • A tiger is as dangerous as a lion. 
 
NOT AS + ADJECTIVE + AS

Difference can also be shown by using not so/as ...as:

  • Mont Blanc is not as high as Mount Everest
  • Norway is not as sunny as Thailand
  • A bicycle is not as expensive as a car

  • Arthur is not as intelligent as Albert

Original source: http://www.edunet.com/english/grammar/ADJECTIVES1.cfm