Rule 2. ‘More’ is used when you compare qualities of a single thing/person. Even if the first adjective is a single syllable word. Examples:
Incorrect – She is smarter than clever.
Correct – She is more smart than clever.
Rule 3. Do not use double comparative adjectives or superlative adjectives. Examples:
Incorrect – These mangoes are more tastier than those.
Correct – These mangoes are tastier than those.