Rules for Comparisons

three syllable or more adjectives : put 'more' in front
expensive ----- more expensive

two syllable adjectives not ending in 'y' : put 'more' in front
stupid ----- more stupid

two syllable adjectives ending in 'y' : replace the 'y' by 'ier'
happy -----happier

one syllable adjectives ending in one vowel and one consonant : double the consonant and add 'er'
big -----bigger

other one syllable adjectives : add 'er'
tall -----taller

Exceptions
good -----better
bad -----worse
far -----further/farther
old -----older/elder
little -----less

With a few exceptions, adverbs normally add 'more'
slowly -----more slowly
easily -----more easily

These are the exceptions
early -----earlier
late -----later
fast -----faster
hard -----harder
near -----nearer
soon -----sooner