1. Regular comparison of adjectives
Comparison with -er/-est
clean - cleaner - (the) cleanest

2. Spelling of the adjectives using the endings -er/-est
large
larger
the largest
leave out the silent -e
big
bigger
the biggest
Double the consonant after short vowel
dirty
dirtier
the dirtiest
Change -y to -i (consonant before -y)
shy
shyer
the shyest
Here -y is not changed to -i. (although consonant before -y)

3. Comparison with more / most
Adjectives with more than one syllable make comparison by adding “MORE” in front of comparative and “MOST” in front of superlative.
Be careful not to add addings –er and –est when forming comparison it this way
difficult - more difficult - (the) most difficult
more difficulter

4. Irregular comparison of adjectives
good
better
the best
bad
worse
the worst
much
more
the most
uncountable nouns
many
countable nouns
little
less
the least

5. Special adjectives positive comparative superlative clever
cleverer / more clever
cleverest / most clever
common
commoner / more common
commonest / most common
likely
likelier / more likely
likeliest / most likely
pleasant
pleasanter / more pleasant
pleasantest / most pleasant
polite
politer / more polite
politest / most polite
quiet
quieter / more quiet
quietest / most quiet
simple
simpler / more simple
simplest / most simple
stupid
stupider / more stupid
stupidest / most stupid
subtle
subtler / more subtle
subtlest / most subtle
sure
surer / more sure
surest / most sure

6. 1. something is similar A=B
Our car is as fast as Peter's car.
2. something is not similar A≠B
2.1. Use not as ... as (to say that something is not similar)
John's car is not as fast as our car. (A≠B)
2.2. Use than 
Our car is faster than John's car. (A>B) John's car is slower than our car. (A<B)

7. Adverbs
Form
In general: adjective + -ly
adjective
adverb
slow
slowly

8. Exceptions in spelling
example
silent e is dropped in true, due, whole
true → truly
y becomes i
happy → happily
le after a consonant is dropped
sensible → sensibly
after ll only add y
full → fully

9. Adjectives ending in -ic: adjective + -ally (exception: public-publicly)
adverb
fantastic
fantastically

10. Exceptions adjective adverb (meaning) good well difficult
with difficulty
public
publicly
deep
deep (place)
direct
hard
high
high (place)
late
most
near
pretty
pretty (=rather)
short

11. Comparison Comparison (-er/-est) Comparative ending in -er
Comparative ending in -er
Superlative ending in -est
one-syllable adverbs (hard)
harder
hardest
adverbs with the same form as adjectives (early)
earlier
earliest

12. Comparison (more / most)
Comparative formed with more
Superlative formed with most
adverbs ending in -ly (happily)
more happily
most happily

13. Irregular comparisons
positive form
comparative
superlative
well
better
best
badly
worse
worst
ill
little
less
least
much
more
most
far (place + time)
further
furthest
far (place)
farther
farthest
late (time)
later
latest