COMPARISON OF EQUALITY

Affirmative: AS - AS
      My son is as tall as me
Negative: NOT SO - AS  (also: not as - as)
      My son isn’t so tall as me / My son isn’t as tall as me

COMPARISON OF INFERIORITY

LESS - THAN
      I’m less fat than last summer
      The film was less interesting than what I expected

COMPARISON OF SUPERIORITY AND SUPERLATIVE

When comparing two things we use the comparative:

      John is taller than Mark

When comparing more than two things, we use the superlative:

      John is the tallest in his family
      Mount Everest is the highest mountain in the world

short words (1 syllable):

Comparatives add -ER and superlatives add -EST
     old  older  oldest
     fast  faster  fastest
Words ending in -e drop it
     late  later  latest
     fine  finer  finest
Words ending in -y change it to -i
     shy  shier  shiest
Words ending in one single syllable followed by one single consonant, double the final consonant when the vowel is stressed: -1V+1C --> -CC
     fat  fatter  fattest
     slim  slimmer  slimmest
 
long words (3 or more syllables):

They use MORE for the comparative and THE MOST for the superlative.
 
     intelligent  more intelligent  the most intelligent
 
2-syllable words:

They can use both forms, but we prefer More/the Most
     
     handsome  more handsome the most handsome
     cheerful  more cheerful  the most cheerful
 
Nevertheless, words ending in -y and some adjectives such as: quiet, clever and narrow usually take -er/-est
     easy  easier   the easiest
     happy  happier  the happiest
     clever  cleverer   the cleverest
 
But if they end in -ly, they use more/most (except: early)
     quickly  more quickly  the most quickly
     slowly  more slowly  the most slowly
     early  earlier  the earliest
 
If you find the two-syllable words confusing, it is usually safe to say that when in doubt, you can always use more/most.

PRONOUNS WITH COMPARATIVES

 If the second part of the comparison is a personal pronoun, there are three possibilities:
     She's older than me     (the most common construction in informal English)
     She's older than I am   (the most common in formal English)
     She's older than I         (very formal and rarely used, so you can forget about it) 

  
SUPERLATIVE SENTENCES

Don't forget to use the article with superlatives: the
     Tommy is the tallest person I know
 
When comparing with a group, use the preposition IN (rarely "of")
     That's the highest building in the world
     You have the nicest room in the hotel
     The boss is the most important person in the company
     I'm the youngest in my family
 
But we can use the preposition OF before plurals and time expresions
     He’s the biggest one of the boys
     Kevin is the most handsome of them
     This is the best day of my life
     July is usually the hottest month of the year

 
GRADING

- my friend is tall  --> my friend is taller than me
- my friend is very tall  --> my friend is much taller than me
- my friend is a bit tall --> my friend is a bit taller than me
- my friend is very very very tall --> my friend is by far the tallest
 
- My friend is much less tall than me
- my friend is by far the tallest in class  (much much taller than the rest)
- my friend is much more intelligent than John
- my girl-friend is by far the most wonderful girl in the world

To express that the quality is increasing, you use more and more

- It's getting darker and darker
- You are becoming more and more stupid

 
Irregular forms

     good/well    better    best
     bad/badly    worse    worst
     far  further/farther    furthest/farthest

 SUMMARY (examples)

=     Jim is as tall as Jack  
≠     Jim is not so tall as Jack 
-      Jim is less tall than Jack
+     Jim is taller than Jack 
       Jim is more intelligent than Jack 
++   Jim is the tallest in my class
       Jim is the most intelligent 

  Note for speakers of Spanish (and Italian, Portuguese, etc.): What you call "superlativo" is not the English superlative (-est), but the forms ending in -ísimo. That form is usually expressed in English with SO:     Marcos es altísimo   Mark is so tall